IMPORTANCE: Seasonal influenza is associated with substantial disease burden. The relationship between census tract-based social vulnerability and clinical outcomes among patients with influenza remains unknown. OBJECTIVE: To characterize associations between social vulnerability and outcomes among patients hospitalized with influenza and to evaluate seasonal influenza vaccine and influenza antiviral utilization patterns across levels of social vulnerability. DESIGN, SETTING, AND PARTICIPANTS: This retrospective repeated cross-sectional study was conducted among adults with laboratory-confirmed influenza-associated hospitalizations from the 2014 to 2015 through the 2018 to 2019 influenza seasons. Data were from a population-based surveillance network of counties within 13 states. Data analysis was conducted in December 2023. EXPOSURE: Census tract-based social vulnerability. MAIN OUTCOMES AND MEASURES: Associations between census tract-based social vulnerability and influenza outcomes (intensive care unit admission, invasive mechanical ventilation and/or extracorporeal membrane oxygenation support, and 30-day mortality) were estimated using modified Poisson regression as adjusted prevalence ratios. Seasonal influenza vaccine and influenza antiviral utilization were also characterized across levels of social vulnerability. RESULTS: Among 57 964 sampled cases, the median (IQR) age was 71 (58-82) years; 55.5% (95% CI, 51.5%-56.0%) were female; 5.2% (5.0%-5.4%) were Asian or Pacific Islander, 18.3% (95% CI, 18.0%-18.6%) were Black or African American, and 64.6% (95% CI, 64.2%-65.0%) were White; and 6.6% (95% CI, 6.4%-68%) were Hispanic or Latino and 74.7% (95% CI, 74.3%-75.0%) were non-Hispanic or Latino. High social vulnerability was associated with higher prevalence of invasive mechanical ventilation and/or extracorporeal membrane oxygenation support (931 of 13 563 unweighted cases; adjusted prevalence ratio [aPR], 1.25 [95% CI, 1.13-1.39]), primarily due to socioeconomic status (790 of 11 255; aPR, 1.31 [95% CI, 1.17-1.47]) and household composition and disability (773 of 11 256; aPR, 1.20 [95% CI, 1.09-1.32]). Vaccination status, presence of underlying medical conditions, and respiratory symptoms partially mediated all significant associations. As social vulnerability increased, the proportion of patients receiving seasonal influenza vaccination declined (-19.4% relative change across quartiles; P < .001) as did the proportion vaccinated by October 31 (-6.8%; P < .001). No differences based on social vulnerability were found in in-hospital antiviral receipt, but early in-hospital antiviral initiation (-1.0%; P = .01) and prehospital antiviral receipt (-17.3%; P < .001) declined as social vulnerability increased. CONCLUSIONS AND RELEVANCE: In this cross-sectional study, social vulnerability was associated with a modestly increased prevalence of invasive mechanical ventilation and/or extracorporeal membrane oxygenation support among patients hospitalized with influenza. Contributing factors may have included worsened baseline respiratory health and reduced receipt of influenza prevention and prehospital or early in-hospital treatment interventions among persons residing in low socioeconomic areas.

BACKGROUND: To protect infants aged <2 months against pertussis, the United States recommends Tdap (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis) vaccination during each pregnancy. Data are limited on the strategy's effectiveness against pertussis in infants aged ≥2 months. METHODS: Pertussis case infants aged 2 to <6 months with cough onset between 1 January 2011 and 31 December 2014 were identified in 6 US states. Controls were 2 to <6 months of age, hospital matched, and selected by birth certificate. Mothers were interviewed to collect demographic and healthcare information. Provider-verified vaccination history was obtained for infants and mothers. Adjusted odds ratios (aORs) were calculated using conditional logistic regression; overall vaccine effectiveness (VE) was estimated as (1 - aOR)×100. To describe maternal Tdap VE modified by infant DTaP (diphtheria and tetanus toxoids and acellular pertussis) doses, case-control sets were unmatched, and a time-to-event analysis was conducted through a generalized linear mixed model. RESULTS: A total of 335 cases and 927 controls were enrolled. The overall adjusted VE estimate for Tdap during pregnancy was 45.6% (95% confidence interval [CI], 5.8%-68.5%) and increased slightly, but not significantly, against infant hospitalization (55.7% [-116.8% to 90.9%]). Although point estimates were not significant, VE was modified by infant DTaP doses (58.8% [95% CI, -6.0% to 84.0%] for 0 DTaP doses, 30.5% [-21.4% to 60.2%] for 1 dose, and 3.2% [-170.8% to 65.4%] for 2 doses). CONCLUSIONS: Our study suggests that there is some benefit of maternal Tdap vaccination beyond the first 2 months of life, however, on-time vaccination of infants remains critical to maintain protection from pertussis.

Annually, tens of thousands of U.S. children and adolescents are hospitalized with seasonal influenza virus infection. Both influenza vaccination and early initiation of antiviral treatment can reduce complications of influenza. Using data from two U.S. influenza surveillance networks for children and adolescents aged <18 years with medically attended, laboratory-confirmed influenza for whom antiviral treatment is recommended, the percentage who received treatment was calculated. Trends in antiviral treatment of children and adolescents hospitalized with influenza from the 2017-18 to the 2023-2024 influenza seasons were also examined. Since 2017-18, when 70%-86% of hospitalized children and adolescents with influenza received antiviral treatment, the proportion receiving treatment notably declined. Among children and adolescents with influenza during the 2023-24 season, 52%-59% of those hospitalized received antiviral treatment. During the 2023-24 season, 31% of those at higher risk for influenza complications seen in the outpatient setting in one network were prescribed antiviral treatment. These findings demonstrate that influenza antiviral treatment is underutilized among children and adolescents who could benefit from treatment. All hospitalized children and adolescents, and those at higher risk for influenza complications in the outpatient setting, should receive antiviral treatment as soon as possible for suspected or confirmed influenza.

BACKGROUND: While the estimated number of U.S. influenza-associated deaths is reported annually, detailed data on the epidemiology of influenza-associated deaths, including the burden of in-hospital versus post-hospital discharge deaths are limited. METHODS: Using data from the 2010-11 through 2018-19 seasons from the Influenza Hospitalization Surveillance Network, we linked cases to death certificates to identify patients who died from any cause during their influenza hospital stay or within 30 days post discharge. We described demographic and clinical characteristics of patients who died in hospital versus post discharge and characterized locations and causes of death (COD). RESULTS: Among 121,390 cases hospitalized with laboratory-confirmed influenza over 9 seasons, 5.5% died; 76% of deaths were in patients ≥65 years, 71% were non-Hispanic White, and 34% had ≥4 underlying medical conditions. Among all patients with an influenza-associated hospitalization who died, 48% of deaths occurred after hospital discharge; the median days from discharge to death was 9 days (IQR 3-19 days). Post-discharge deaths more often occurred in older patients and among those with underlying medical conditions. Only 37% of patients who died had "influenza" as a COD on their death certificate. Influenza was more frequently listed as a COD among persons who died in-hospital compared with cardiovascular disease among those who died after discharge. CONCLUSIONS: All-cause mortality burden is substantial among patients hospitalized with influenza, with almost 50% of deaths occurring within 30 days after hospital discharge. Surveillance systems should consider capture of post-discharge outcomes to better characterize the impact of influenza on all-cause mortality.

BACKGROUND: Screening for SARS-CoV-2 infection among hospital admissions made interpretation of COVID-19 hospitalization data challenging as SARS-CoV-2-positive persons with mild or asymptomatic infection may be incorrectly identified as COVID-19-associated hospitalizations. The study objective is to estimate the proportion of hospitalizations likely attributable to COVID-19 among SARS-CoV-2-positive hospitalized patients. METHODS: A sample of laboratory-confirmed SARS-CoV-2-positive hospitalizations from the COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) from June 2020 to September 2023 was analyzed, with a focus on July 2022 to September 2023. Likely COVID-19-attributable hospitalizations were defined as hospitalizations among SARS-CoV-2-positive non-pregnant adults ages ≥ 18 years with COVID-19-related presenting complaint, treatment, or discharge diagnosis. RESULTS: Among 44,816 sampled hospitalizations, 90% met the definition of likely COVID-19-attributable. Among the 9866 admissions occurring during July 2022 to September 2023, 86% were likely COVID-19-attributable; 87% had a COVID-19-related presenting complaint, 64% received steroids or COVID-19-related treatment, 47% had respiratory- and 10% had coagulopathy-related discharge diagnoses, and 39% had COVID-19 as the principal discharge diagnosis code. More than 70% met ≥ 2 criteria. Compared with likely COVID-19-attributable hospitalizations, SARS-CoV-2-positive patients who did not meet the case definition were more likely to be ages 18-49 years (27% vs. 13%), have no underlying medical conditions (14% vs. 4%), or be asymptomatic for COVID-19 upon admission (46% vs. 10%) (all p < 0.05). CONCLUSIONS: Most hospitalizations among SARS-CoV-2-positive adults in a recent period were likely attributable to COVID-19. COVID-19-attributable hospitalizations are less common among younger SARS-CoV-2-positive hospitalized adults but still account for nearly three quarters of all admissions among SARS-CoV-2-positive adults in this age group.

PROBLEM/CONDITION: Seasonal influenza accounts for 9.3 million-41 million illnesses, 100,000-710,000 hospitalizations, and 4,900-51,000 deaths annually in the United States. Since 2003, the Influenza Hospitalization Surveillance Network (FluSurv-NET) has been conducting population-based surveillance for laboratory-confirmed influenza-associated hospitalizations in the United States, including weekly rate estimations and descriptions of clinical characteristics and outcomes for hospitalized patients. However, a comprehensive summary of trends in hospitalization rates and clinical data collected from the surveillance platform has not been available. REPORTING PERIOD: 2010-11 through 2022-23 influenza seasons. DESCRIPTION OF SYSTEM: FluSurv-NET conducts population-based surveillance for laboratory-confirmed influenza-associated hospitalizations among children and adults. During the reporting period, the surveillance network included 13-16 participating sites each influenza season, with prespecified geographic catchment areas that covered 27 million-29 million persons and included an estimated 8.8%-9.5% of the U.S. population. A case was defined as a person residing in the catchment area within one of the participating states who had a positive influenza laboratory test result within 14 days before or at any time during their hospitalization. Each site abstracted case data from hospital medical records into a standardized case report form, with selected variables submitted to CDC on a weekly basis for rate estimations. Weekly and cumulative laboratory-confirmed influenza-associated hospitalization rates per 100,000 population were calculated for each season from 2010-11 through 2022-23 and stratified by patient age (0-4 years, 5-17 years, 18-49 years, 50-64 years, and ≥65 years), sex, race and ethnicity, influenza type, and influenza A subtype. During the 2020-21 season, only the overall influenza hospitalization rate was reported because case counts were insufficient to estimate stratified rates. RESULTS: During the 2010-11 to 2022-23 influenza seasons, laboratory-confirmed influenza-associated hospitalization rates varied significantly across seasons. Before the COVID-19 pandemic, hospitalization rates per 100,000 population ranged from 8.7 (2011-12) to 102.9 (2017-18) and had consistent seasonality. After SARS-CoV-2 emerged, the hospitalization rate for 2020-21 was 0.8, and the rate did not return to recent prepandemic levels until 2022-23. Inconsistent seasonality also was observed during 2020-21 through 2022-23, with influenza activity being very low during 2020-21, extending later than usual during 2021-22, and occurring early during 2022-23. Molecular assays, particularly multiplex standard molecular assays, were the most common influenza test type in recent seasons, increasing from 12% during 2017-18 for both pediatric and adult cases to 43% and 55% during 2022-23 for pediatric and adult cases, respectively. During each season, adults aged ≥65 years consistently had the highest influenza-associated hospitalization rate across all age groups, followed in most seasons by children aged 0-4 years. Black or African American and American Indian or Alaska Native persons had the highest age-adjusted influenza-associated hospitalization rates across these seasons. Among patients hospitalized with influenza, the prevalence of at least one underlying medical condition increased with increasing age, ranging from 36.9% among children aged 0-4 years to 95.4% among adults aged ≥65 years. Consistently across each season, the most common underlying medical conditions among children and adolescents were asthma, neurologic disorders, and obesity. The most common underlying medical conditions among adults were hypertension, obesity, chronic metabolic disease, chronic lung disease, and cardiovascular disease. The proportion of FluSurv-NET patients with acute respiratory signs and symptoms at hospital admission decreased from 90.6% during 2018-19 to 83.2% during 2022-23. Although influenza antiviral use increased during the 2010-11 through the 2017-18 influenza seasons, it decreased from 90.2% during 2018-19 to 79.1% during 2022-23, particularly among children and adolescents. Admission to the intensive care unit, need for invasive mechanical ventilation, and in-hospital death ranged from 14.1% to 22.3%, 4.9% to 11.1%, and 2.2% to 3.5% of patients hospitalized with influenza, respectively, during the reported surveillance period. INTERPRETATIONS: Influenza continues to cause severe morbidity and mortality, particularly in older adults, and disparities have persisted in racial and ethnic minority groups. Persons with underlying medical conditions represented a large proportion of patients hospitalized with influenza. Increased use of multiplex tests and other potential changes in facility-level influenza testing practices (e.g., influenza screening at all hospital admissions) could have implications for the detection of influenza infections among hospitalized patients. Antiviral use decreased in recent seasons, and explanations for the decrease should be further evaluated. PUBLIC HEALTH ACTION: Continued robust influenza surveillance is critical to monitor progress in efforts to encourage antiviral treatment and improve clinical outcomes for persons hospitalized with influenza. In addition, robust influenza surveillance can potentially reduce disparities by informing efforts to increase access to preventive measures for influenza and monitoring any subsequent changes in hospitalization rates.

Among adults, COVID-19 hospitalization rates increase with age. Data from the COVID-19-Associated Hospitalization Surveillance Network were analyzed to estimate population-based COVID-19-associated hospitalization rates during October 2023-April 2024 and identify demographic and clinical characteristics of adults aged ≥18 years hospitalized with COVID-19. Adults aged ≥65 years accounted for 70% of all adult COVID-19-associated hospitalizations, and their COVID-19-associated hospitalization rates were higher than those among younger adult age groups. Cumulative rates of COVID-19-associated hospitalization during October 2023-April 2024 were the lowest for all adult age groups during an October-April surveillance period since 2020-2021. However, hospitalization rates among all adults aged ≥75 years approached one COVID-19-associated hospitalization for every 100 persons. Among adults hospitalized with COVID-19, 88.1% had not received the 2023-2024 formula COVID-19 vaccine before hospitalization, 80.0% had multiple underlying medical conditions, and 16.6% were residents of long-term care facilities (LTCFs). Guidance for adults at high risk for severe COVID-19 illness, including adults aged ≥65 years and residents of LTCFs, should continue to focus on adopting measures to reduce risk for contracting COVID-19, advocating for receipt of recommended COVID-19 vaccinations, and seeking prompt outpatient antiviral treatment after receipt of a positive SARS-CoV-2 test result.

BACKGROUND: Pneumonia is common in adults hospitalized with laboratory-confirmed influenza, but the association between timeliness of influenza antiviral treatment and severe clinical outcomes in patients with influenza-associated pneumonia is not well characterized. METHODS: We included adults aged ≥18 years hospitalized with laboratory-confirmed influenza and a discharge diagnosis of pneumonia over 7 influenza seasons (2012-2019) sampled from a multi-state population-based surveillance network. We evaluated 3 treatment groups based on timing of influenza antiviral initiation relative to admission date (day 0, day 1, days 2-5). Baseline characteristics and clinical outcomes were compared across groups using unweighted counts and weighted percentages accounting for the complex survey design. Logistic regression models were generated to evaluate the association between delayed treatment and 30-day all-cause mortality. RESULTS: 26,233 adults were sampled in the analysis. Median age was 71 years and most (92.2%) had ≥1 non-immunocompromising condition. Overall, 60.9% started antiviral treatment on day 0, 29.5% on day 1, and 9.7% on days 2-5 (median 2 days). Baseline characteristics were similar across groups. Thirty-day mortality occurred in 7.5%, 8.5%, and 10.2% of patients who started treatment on day 0, day 1, and days 2-5, respectively. Compared to those treated on day 0, adjusted OR for death was 1.14 (95%CI: 1.01-1.27) in those starting treatment on day 1 and 1.40 (95%CI: 1.17-1.66) in those starting on days 2-5. DISCUSSION: Delayed initiation of antiviral treatment in patients hospitalized with influenza-associated pneumonia was associated with higher risk of death, highlighting the importance of timely initiation of antiviral treatment at admission.

IMPORTANCE: Respiratory syncytial virus (RSV) infection can cause severe respiratory illness in older adults. Less is known about the cardiac complications of RSV disease compared with those of influenza and SARS-CoV-2 infection. OBJECTIVE: To describe the prevalence and severity of acute cardiac events during hospitalizations among adults aged 50 years or older with RSV infection. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study analyzed surveillance data from the RSV Hospitalization Surveillance Network, which conducts detailed medical record abstraction among hospitalized patients with RSV infection detected through clinician-directed laboratory testing. Cases of RSV infection in adults aged 50 years or older within 12 states over 5 RSV seasons (annually from 2014-2015 through 2017-2018 and 2022-2023) were examined to estimate the weighted period prevalence and 95% CIs of acute cardiac events. EXPOSURES: Acute cardiac events, identified by International Classification of Diseases, 9th Revision, Clinical Modification or International Statistical Classification of Diseases, Tenth Revision, Clinical Modification discharge codes, and discharge summary review. MAIN OUTCOMES AND MEASURES: Severe disease outcomes, including intensive care unit (ICU) admission, receipt of invasive mechanical ventilation, or in-hospital death. Adjusted risk ratios (ARR) were calculated to compare severe outcomes among patients with and without acute cardiac events. RESULTS: The study included 6248 hospitalized adults (median [IQR] age, 72.7 [63.0-82.3] years; 59.6% female; 56.4% with underlying cardiovascular disease) with laboratory-confirmed RSV infection. The weighted estimated prevalence of experiencing a cardiac event was 22.4% (95% CI, 21.0%-23.7%). The weighted estimated prevalence was 15.8% (95% CI, 14.6%-17.0%) for acute heart failure, 7.5% (95% CI, 6.8%-8.3%) for acute ischemic heart disease, 1.3% (95% CI, 1.0%-1.7%) for hypertensive crisis, 1.1% (95% CI, 0.8%-1.4%) for ventricular tachycardia, and 0.6% (95% CI, 0.4%-0.8%) for cardiogenic shock. Adults with underlying cardiovascular disease had a greater risk of experiencing an acute cardiac event relative to those who did not (33.0% vs 8.5%; ARR, 3.51; 95% CI, 2.85-4.32). Among all hospitalized adults with RSV infection, 18.6% required ICU admission and 4.9% died during hospitalization. Compared with patients without an acute cardiac event, those who experienced an acute cardiac event had a greater risk of ICU admission (25.8% vs 16.5%; ARR, 1.54; 95% CI, 1.23-1.93) and in-hospital death (8.1% vs 4.0%; ARR, 1.77; 95% CI, 1.36-2.31). CONCLUSIONS AND RELEVANCE: In this cross-sectional study over 5 RSV seasons, nearly one-quarter of hospitalized adults aged 50 years or older with RSV infection experienced an acute cardiac event (most frequently acute heart failure), including 1 in 12 adults (8.5%) with no documented underlying cardiovascular disease. The risk of severe outcomes was nearly twice as high in patients with acute cardiac events compared with patients who did not experience an acute cardiac event. These findings clarify the baseline epidemiology of potential cardiac complications of RSV infection prior to RSV vaccine availability.

BACKGROUND: Respiratory syncytial virus (RSV) can cause severe disease among infants and older adults. Less is known about RSV among pregnant women. METHODS: To analyze hospitalizations with laboratory-confirmed RSV among women aged 18 to 49 years, we used data from the RSV Hospitalization Surveillance Network (RSV-NET), a multistate population-based surveillance system. Specifically, we compared characteristics and outcomes among (1) pregnant and nonpregnant women during the pre-COVID-19 pandemic period (2014-2018), (2) pregnant women with respiratory symptoms during the prepandemic and pandemic periods (2021-2023), and (3) pregnant women with and without respiratory symptoms in the pandemic period. Using multivariable logistic regression, we examined whether pregnancy was a risk factor for severe outcomes (intensive care unit admission or in-hospital death) among women aged 18 to 49 years who were hospitalized with RSV prepandemic. RESULTS: Prepandemic, 387 women aged 18 to 49 years were hospitalized with RSV. Of those, 350 (90.4%) had respiratory symptoms, among whom 33 (9.4%) were pregnant. Five (15.2%) pregnant women and 74 (23.3%) nonpregnant women were admitted to the intensive care unit; no pregnant women and 5 (1.6%) nonpregnant women died. Among 279 hospitalized pregnant women, 41 were identified prepandemic and 238 during the pandemic: 80.5% and 35.3% had respiratory symptoms, respectively (P < .001). Pregnant women were more likely to deliver during their RSV-associated hospitalization during the pandemic vs the prepandemic period (73.1% vs 43.9%, P < .001). CONCLUSIONS: Few pregnant women had severe RSV disease, and pregnancy was not a risk factor for a severe outcome. More asymptomatic pregnant women were identified during the pandemic, likely due to changes in testing practices for RSV.

BACKGROUND: Older age and chronic conditions are associated with severe influenza outcomes; however, data are only comprehensively available for adults ≥65 years old. Using data from the Influenza Hospitalization Surveillance Network (FluSurv-NET), we identified characteristics associated with severe outcomes in adults 18-49 years old hospitalized with influenza. METHODS: We included FluSurv-NET data from nonpregnant adults 18-49 years old hospitalized with laboratory-confirmed influenza during the 2011-2012 through 2018-2019 seasons. We used bivariate and multivariable logistic regression to determine associations between select characteristics and severe outcomes including intensive care unit (ICU) admission, invasive mechanical ventilation (IMV), and in-hospital death. RESULTS: A total of 16 140 patients aged 18-49 years and hospitalized with influenza were included in the analysis; the median age was 39 years, and 26% received current-season influenza vaccine before hospitalization. Obesity, asthma, and diabetes mellitus were the most common chronic conditions. Conditions associated with a significantly increased risk of severe outcomes included age group 30-39 or 40-49 years (IMV, age group 30-39 years: adjusted odds ratio [aOR], 1.25; IMV, age group 40-49 years: aOR, 1.36; death, age group 30-39 years: aOR, 1.28; death, age group 40-49 years: aOR, 1.69), being unvaccinated (ICU: aOR, 1.18; IMV: aOR, 1.25; death: aOR, 1.48), and having chronic conditions including extreme obesity and chronic lung, cardiovascular, metabolic, neurologic, or liver diseases (ICU: range aOR, 1.22-1.56; IMV: range aOR, 1.17-1.54; death: range aOR, 1.43-2.36). CONCLUSIONS: To reduce the morbidity and mortality associated with influenza among adults aged 18-49 years, health care providers should strongly encourage receipt of annual influenza vaccine and lifestyle/behavioral modifications, particularly among those with chronic medical conditions.

BACKGROUND: Influenza burden varies across seasons, partly due to differences in circulating influenza virus types or subtypes. Using data from the US population-based surveillance system, Influenza Hospitalization Surveillance Network (FluSurv-NET), we aimed to assess the severity of influenza-associated outcomes in individuals hospitalised with laboratory-confirmed influenza virus infections during the 2010-11 to 2018-19 influenza seasons. METHODS: To evaluate the association between influenza virus type or subtype causing the infection (influenza A H3N2, A H1N1pdm09, and B viruses) and in-hospital severity outcomes (intensive care unit [ICU] admission, use of mechanical ventilation or extracorporeal membrane oxygenation [ECMO], and death), we used FluSurv-NET to capture data for laboratory-confirmed influenza-associated hospitalisations from the 2010-11 to 2018-19 influenza seasons for individuals of all ages living in select counties in 13 US states. All individuals had to have an influenza virus test within 14 days before or during their hospital stay and an admission date between Oct 1 and April 30 of an influenza season. Exclusion criteria were individuals who did not have a complete chart review; cases from sites that contributed data for three or fewer seasons; hospital-onset cases; cases with unidentified influenza type; cases of multiple influenza virus type or subtype co-infection; or individuals younger than 6 months and ineligible for the influenza vaccine. Logistic regression models adjusted for influenza season, influenza vaccination status, age, and FluSurv-NET site compared odds of in-hospital severity by virus type or subtype. When missing, influenza A subtypes were imputed using chained equations of known subtypes by season. FINDINGS: Data for 122 941 individuals hospitalised with influenza were captured in FluSurv-NET from the 2010-11 to 2018-19 seasons; after exclusions were applied, 107 941 individuals remained and underwent influenza A virus imputation when missing A subtype (43·4%). After imputation, data for 104 969 remained and were included in the final analytic sample. Averaging across imputed datasets, 57·7% (weighted percentage) had influenza A H3N2, 24·6% had influenza A H1N1pdm09, and 17·7% had influenza B virus infections; 16·7% required ICU admission, 6·5% received mechanical ventilation or ECMO, and 3·0% died (95% CIs had a range of less than 0·1% and are not displayed). Individuals with A H1N1pdm09 had higher odds of in-hospital severe outcomes than those with A H3N2: adjusted odds ratios (ORs) for A H1N1pdm09 versus A H3N2 were 1·42 (95% CI 1·32-1·52) for ICU admission; 1·79 (1·60-2·00) for mechanical ventilation or ECMO use; and 1·25 (1·07-1·46) for death. The adjusted ORs for individuals infected with influenza B versus influenza A H3N2 were 1·06 (95% CI 1·01-1·12) for ICU admission, 1·14 (1·05-1·24) for mechanical ventilation or ECMO use, and 1·18 (1·07-1·31) for death. INTERPRETATION: Despite a higher burden of hospitalisations with influenza A H3N2, we found an increased likelihood of in-hospital severe outcomes in individuals hospitalised with influenza A H1N1pdm09 or influenza B virus. Thus, it is important for individuals to receive an annual influenza vaccine and for health-care providers to provide early antiviral treatment for patients with suspected influenza who are at increased risk of severe outcomes, not only when there is high influenza A H3N2 virus circulation but also when influenza A H1N1pdm09 and influenza B viruses are circulating. FUNDING: The US Centers for Disease Control and Prevention.

Background The COVID-19 pandemic has caused substantial morbidity and mortality.Objectives To describe monthly demographic and clinical trends among adults hospitalized with COVID-19.Design Pooled cross-sectional.Setting 99 counties within 14 states participating in the Coronavirus Disease 2019-Associated Hospitalization Surveillance Network (COVID-NET).Patients U.S. adults (aged ≥18 years) hospitalized with laboratory-confirmed COVID-19 during March 1-December 31, 2020.Measurements Monthly trends in weighted percentages of interventions and outcomes including length of stay (LOS), intensive care unit admissions (ICU), invasive mechanical ventilation (IMV), vasopressor use and in-hospital death (death). Monthly hospitalization, ICU and death rates per 100,000 population.Results Among 116,743 hospitalized adults, median age was 62 years. Among 18,508 sampled adults, median LOS decreased from 6.4 (March) to 4.6 days (December). Remdesivir and systemic corticosteroid use increased from 1.7% and 18.9% (March) to 53.8% and 74.2% (December), respectively. Frequency of ICU decreased from 37.8% (March) to 20.5% (December). IMV (27.8% to 8.7%), vasopressors (22.7% to 8.8%) and deaths (13.9% to 8.7%) decreased from March to October; however, percentages of these interventions and outcomes remained stable or increased in November and December. Percentage of deaths significantly decreased over time for non-Hispanic White patients (p-value &lt;0.01) but not non-Hispanic Black or Hispanic patients. Rates of hospitalization (105.3 per 100,000), ICU (20.2) and death (11.7) were highest during December.Limitations COVID-NET covers approximately 10% of the U.S. population; findings may not be generalizable to the entire country.Conclusions After initial improvement during April-October 2020, trends in interventions and outcomes worsened during November-December, corresponding with the 3rd peak of the U.S. pandemic. These data provide a longitudinal assessment of trends in COVID-19-associated outcomes prior to widespread COVID-19 vaccine implementation.Competing Interest StatementDr. Evan Anderson reports grants from Pfizer, grants from Merck, grants from PaxVax, grants from Micron, grants from Sanofi-Pasteur, grants from Janssen, grants from MedImmune, grants from GSK, personal fees from Sanofi-Pasteur, personal fees from Pfizer, personal fees from Medscape, personal fees from Kentucky Bioprocessing, Inc, personal fees from Sanofi-Pasteur, outside the submitted work. Dr. William Schaffner reports personal fees from VBI Vaccines, outside the submitted work. Funding StatementThis work was supported by the Centers of Disease Control and Prevention through an Emerging Infections Program cooperative agreement (grant CK17-1701) and through a Council of State and Territorial Epidemiologists cooperative agreement (grant NU38OT000297-02-00).Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy. Sites participating in COVID-NET obtained approval from their respective state and local Institutional Review Boards, as applicable.All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).YesI have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting check ist(s) and other pertinent material as supplementary files, if applicable.YesPublicly available data referred to in this analysis can be found at: https://gis.cdc.gov/grasp/covidnet/covid19_3.html https://gis.cdc.gov/grasp/covidnet/covid19_3.html

Background As of August 21, 2021, &gt;60% of the U.S. population aged ≥18 years were fully vaccinated with vaccines highly effective in preventing hospitalization due to Coronavirus Disease-2019 (COVID-19). Infection despite full vaccination (vaccine breakthrough) has been reported, but characteristics of those with vaccine breakthrough resulting in hospitalization and relative rates of hospitalization in unvaccinated and vaccinated persons are not well described, including during late June and July 2021 when the highly transmissible Delta variant predominated.Methods From January 1–June 30, 2021, cases defined as adults aged ≥18 years with laboratory-confirmed Severe Acute Respiratory Coronavirus-2 (SARS-CoV-2) infection were identified from &gt;250 acute care hospitals in the population-based COVID-19-Associated Hospitalization Surveillance Network (COVID-NET). Through chart review for sampled cases, we examine characteristics associated with vaccination breakthrough. From January 24–July 24, 2021, state immunization information system data linked to both &gt;37,000 cases representative cases and the defined surveillance catchment area population were used to compare weekly hospitalization rates in vaccinated and unvaccinated individuals. Unweighted case counts and weighted percentages are presented.Results From January 1 – June 30, 2021, fully vaccinated cases increased from 1 (0.01%) to 321 (16.1%) per month. Among 4,732 sampled cases, fully vaccinated persons admitted with COVID-19 were older compared with unvaccinated persons (median age 73 years [Interquartile Range (IQR) 65-80] v. 59 years [IQR 48-70]; p&lt;0.001), more likely to have 3 or more underlying medical conditions (201 (70.8%) v. 2,305 (56.1%), respectively; p&lt;0.001) and be residents of long-term care facilities [37 (14.5%) v. 146 (5.5%), respectively; p&lt;0.001]. From January 24 – July 24, 2021, cumulative hospitalization rates were 17 times higher in unvaccinated persons compared with vaccinated persons (423 cases per 100,000 population v. 26 per 100,000 population, respectively); rate ratios were 23, 22 and 13 for those aged 18-49, 50-64, and ≥65 years respectively. For June 27 – July 24, hospitalization rates were ≥10 times higher in unvaccinated persons compared with vaccinated persons for all age groups across all weeks.Conclusion Population-based hospitalization rates show that unvaccinated adults aged ≥18 years are 17 times more likely to be hospitalized compared with vaccinated adults. Rates are far higher in unvaccinated persons in all adult age groups, including during a period when the Delta variant was the predominant strain of the SARS-CoV-2 virus. Vaccines continue to play a critical role in preventing serious COVID-19 illness and remain highly effective in preventing COVID-19 hospitalizations.Competing Interest StatementAll authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Evan J. Anderson reports grants from Pfizer, grants from Merck, grants from PaxVax, grants from Micron, grants from Sanofi-Pasteur, grants from Janssen, grants from MedImmune, grants from GSK, personal fees from Sanofi-Pasteur, personal fees from Pfizer, personal fees from Medscape, personal fees from Kentucky Bioprocessing, Inc, personal fees from Sanofi-Pasteur, personal fees from Janssen, outside the submitted work; and his institution has also received funding from NIH to conduct clinical trials of Moderna and Janssen COVID-19 vaccines. Ruth Lynfield reports Associate Editor for American Academy of Pediatrics Red Book (Committee on Infectious Diseases), donated fee to Minnesota Department of Health. Laurie M. Billing reports grants from Council of State and Territorial Epidemiologists (CSTE), during the conduct of the study; grants from Centers for Disease Control and Prevention (CDC) outside the submitted work. William Schaffner reports personal fees from VBI Vaccines, outside the submitted work. No other potential conflicts of interest were disclosed.Funding StatementThis work was supported by the Centers of Disease Control and Prevention through an Emerging Infections Program cooperative agreement (grant CK17-1701) and through a Council of State and Territorial Epidemiologists cooperative agreement (grant NU38OT000297-02-00).Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy (see e.g., 45 C.F.R. part 46.102(l)(2), 21 C.F.R. part 56; 42 U.S.C. 241(d); 5 U.S.C.All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).YesI have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.YesPublicly available data referred to in this analysis can be found at: https://gis.cdc.gov/grasp/covidnet/covid19_3.html https://gis.cdc.gov/grasp/COVIDNet/COVID19_5.html https://gis.cdc.gov/grasp/covidnet/covid19_3.html https://gis.cdc.gov/grasp/COVIDNet/COVID19_5.html

In mid-June 2021, B.1.671.2 (Delta) became the predominant variant of SARS-CoV-2, the virus that causes COVID-19, circulating in the United States. As of July 2021, the Delta variant was responsible for nearly all new SARS-CoV-2 infections in the United States.* The Delta variant is more transmissible than previously circulating SARS-CoV-2 variants (1); however, whether it causes more severe disease in adults has been uncertain. Data from the CDC COVID-19-Associated Hospitalization Surveillance Network (COVID-NET), a population-based surveillance system for COVID-19-associated hospitalizations, were used to examine trends in severe outcomes in adults aged ≥18 years hospitalized with laboratory-confirmed COVID-19 during periods before (January-June 2021) and during (July-August 2021) Delta variant predominance. COVID-19-associated hospitalization rates among all adults declined during January-June 2021 (pre-Delta period), before increasing during July-August 2021 (Delta period). Among sampled nonpregnant hospitalized COVID-19 patients with completed medical record abstraction and a discharge disposition during the pre-Delta period, the proportion of patients who were admitted to an intensive care unit (ICU), received invasive mechanical ventilation (IMV), or died while hospitalized did not significantly change from the pre-Delta period to the Delta period. The proportion of hospitalized COVID-19 patients who were aged 18-49 years significantly increased, from 24.7% (95% confidence interval [CI] = 23.2%-26.3%) of all hospitalizations in the pre-Delta period, to 35.8% (95% CI = 32.1%-39.5%, p<0.01) during the Delta period. When examined by vaccination status, 71.8% of COVID-19-associated hospitalizations in the Delta period were in unvaccinated adults. Adults aged 18-49 years accounted for 43.6% (95% CI = 39.1%-48.2%) of all hospitalizations among unvaccinated adults during the Delta period. No difference was observed in ICU admission, receipt of IMV, or in-hospital death among nonpregnant hospitalized adults between the pre-Delta and Delta periods. However, the proportion of unvaccinated adults aged 18-49 years hospitalized with COVID-19 has increased as the Delta variant has become more predominant. Lower vaccination coverage in this age group likely contributed to the increase in hospitalized patients during the Delta period. COVID-19 vaccination is critical for all eligible adults, including those aged <50 years who have relatively low vaccination rates compared with older adults.

From surveillance data of patients hospitalized with laboratory-confirmed influenza in the United States during the 2015-2016 through 2018-2019 seasons, initiation of antiviral treatment increased from 86% to 94%, with increases seen across all age groups. However, 62% started therapy ≥3 days after illness onset, driven by late presentation to care.

BACKGROUND: Influenza is a persistent public health problem associated with severe morbidity and mortality. Drug use is related to myriad health complications, but the relationship between drug use and severe influenza outcomes is not well understood. The study objective was to evaluate the relationship between drug use and severe influenza-associated outcomes. METHODS: Data were collected by the Influenza Hospitalization Surveillance Network (FluSurv-NET) from the 2016-2017 through 2018-2019 influenza seasons. Among persons hospitalized with influenza, descriptive statistics and logistic regression models were used to analyze differences in demographic characteristics, risk and behavioral factors, and severe outcomes (intensive care unit [ICU] admission, mechanical ventilation, or death) between people who use drugs (PWUD), defined as having documented drug use within the past year, and non-PWUD. RESULTS: Among 48,430 eligible hospitalized influenza cases, 2019 were PWUD and 46,411 were non-PWUD. PWUD were younger than non-PWUD and more likely to be male, non-Hispanic Black or Hispanic/Latino, smoke tobacco, abuse alcohol, and have chronic conditions including asthma, chronic liver disease, chronic lung disease, or immunosuppressive conditions. PWUD had greater odds of ICU admission and mechanical ventilation, but not death compared with non-PWUD; however, these findings were not statistically significant after adjustment. Opioid use specifically was associated with increased risk of ICU admission and mechanical ventilation. CONCLUSION: These results support targeted initiatives to prevent influenza in this population, including influenza vaccination, which remains one of the most important tools to prevent influenza infection and associated severe outcomes.

IMPORTANCE: Understanding risk factors for hospitalization in vaccinated persons and the association of COVID-19 vaccines with hospitalization rates is critical for public health efforts to control COVID-19. OBJECTIVE: To determine characteristics of COVID-19-associated hospitalizations among vaccinated persons and comparative hospitalization rates in unvaccinated and vaccinated persons. DESIGN, SETTING, AND PARTICIPANTS: From January 1, 2021, to April 30, 2022, patients 18 years or older with laboratory-confirmed SARS-CoV-2 infection were identified from more than 250 hospitals in the population-based COVID-19-Associated Hospitalization Surveillance Network. State immunization information system data were linked to cases, and the vaccination coverage data of the defined catchment population were used to compare hospitalization rates in unvaccinated and vaccinated individuals. Vaccinated and unvaccinated patient characteristics were compared in a representative sample with detailed medical record review; unweighted case counts and weighted percentages were calculated. EXPOSURES: Laboratory-confirmed COVID-19-associated hospitalization, defined as a positive SARS-CoV-2 test result within 14 days before or during hospitalization. MAIN OUTCOMES AND MEASURES: COVID-19-associated hospitalization rates among vaccinated vs unvaccinated persons and factors associated with COVID-19-associated hospitalization in vaccinated persons were assessed. RESULTS: Using representative data from 19509 hospitalizations (see Table 1 for demographic information), monthly COVID-19-associated hospitalization rates ranged from 3.5 times to 17.7 times higher in unvaccinated persons than vaccinated persons regardless of booster dose status. From January to April 2022, when the Omicron variant was predominant, hospitalization rates were 10.5 times higher in unvaccinated persons and 2.5 times higher in vaccinated persons with no booster dose, respectively, compared with those who had received a booster dose. Among sampled cases, vaccinated hospitalized patients with COVID-19 were older than those who were unvaccinated (median [IQR] age, 70 [58-80] years vs 58 [46-70] years, respectively; P<.001) and more likely to have 3 or more underlying medical conditions (1926 [77.8%] vs 4124 [51.6%], respectively; P<.001). CONCLUSIONS AND RELEVANCE: In this cross-sectional study of US adults hospitalized with COVID-19, unvaccinated adults were more likely to be hospitalized compared with vaccinated adults; hospitalization rates were lowest in those who had received a booster dose. Hospitalized vaccinated persons were older and more likely to have 3 or more underlying medical conditions and be long-term care facility residents compared with hospitalized unvaccinated persons. The study results suggest that clinicians and public health practitioners should continue to promote vaccination with all recommended doses for eligible persons.

Immunocompromised persons are at increased risk for severe COVID-19-related outcomes, including intensive care unit (ICU) admission and death (1). Data on adults aged ≥18 years hospitalized with laboratory-confirmed COVID-19 from 10 U.S. states in the COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) were analyzed to assess associations between immunocompromise and ICU admission and in-hospital death during March 1, 2020-February 28, 2022. Associations of COVID-19 vaccination status with ICU admission and in-hospital death were also examined during March 1, 2021-February 28, 2022. During March 1, 2020-February 28, 2022, among a sample of 22,345 adults hospitalized for COVID-19, 12.2% were immunocompromised. Among unvaccinated patients, those with immunocompromise had higher odds of ICU admission (adjusted odds ratio [aOR] = 1.26; 95% CI = 1.08-1.49) and in-hospital death (aOR = 1.34; 95% CI = 1.05-1.70) than did nonimmunocompromised patients. Among vaccinated patients,* those with immunocompromise had higher odds of ICU admission (aOR = 1.40; 95% CI = 1.01-1.92) and in-hospital death (aOR = 1.87; 95% CI = 1.28-2.75) than did nonimmunocompromised patients. During March 1, 2021-February 28, 2022, among nonimmunocompromised patients, patients who were vaccinated had lower odds of death (aOR = 0.58; 95% CI = 0.39-0.86) than did unvaccinated patients; among immunocompromised patients, odds of death between vaccinated and unvaccinated patients did not differ. Immunocompromised persons need additional protection from COVID-19 and using multiple known COVID-19 prevention strategies,(†) including nonpharmaceutical interventions, up-to-date vaccination of immunocompromised persons and their close contacts,(§) early testing, and COVID-19 prophylactic (Evusheld) and early antiviral treatment,(¶) can help prevent hospitalization and subsequent severe COVID-19 outcomes among immunocompromised persons.

The B.1.1.529 (Omicron) variant of SARS-CoV-2, the virus that causes COVID-19, has been the predominant circulating variant in the United States since late December 2021.* Coinciding with increased Omicron circulation, COVID-19-associated hospitalization rates increased rapidly among infants and children aged 0-4 years, a group not yet eligible for vaccination (1). Coronavirus Disease 19-Associated Hospitalization Surveillance Network (COVID-NET)(†) data were analyzed to describe COVID-19-associated hospitalizations among U.S. infants and children aged 0-4 years since March 2020. During the period of Omicron predominance (December 19, 2021-February 19, 2022), weekly COVID-19-associated hospitalization rates per 100,000 infants and children aged 0-4 years peaked at 14.5 (week ending January 8, 2022); this Omicron-predominant period peak was approximately five times that during the period of SARS-CoV-2 B.1.617.2 (Delta) predominance (June 27-December 18, 2021, which peaked the week ending September 11, 2021).(§) During Omicron predominance, 63% of hospitalized infants and children had no underlying medical conditions; infants aged <6 months accounted for 44% of hospitalizations, although no differences were observed in indicators of severity by age. Strategies to prevent COVID-19 among infants and young children are important and include vaccination among currently eligible populations (2) such as pregnant women (3), family members, and caregivers of infants and young children (4).

The first U.S. case of COVID-19 attributed to the Omicron variant of SARS-CoV-2 (the virus that causes COVID-19) was reported on December 1, 2021 (1), and by the week ending December 25, 2021, Omicron was the predominant circulating variant in the United States.* Although COVID-19-associated hospitalizations are more frequent among adults,(†) COVID-19 can lead to severe outcomes in children and adolescents (2). This report analyzes data from the Coronavirus Disease 19-Associated Hospitalization Surveillance Network (COVID-NET)(§) to describe COVID-19-associated hospitalizations among U.S. children (aged 0-11 years) and adolescents (aged 12-17 years) during periods of Delta (July 1-December 18, 2021) and Omicron (December 19, 2021-January 22, 2022) predominance. During the Delta- and Omicron-predominant periods, rates of weekly COVID-19-associated hospitalizations per 100,000 children and adolescents peaked during the weeks ending September 11, 2021, and January 8, 2022, respectively. The Omicron variant peak (7.1 per 100,000) was four times that of the Delta variant peak (1.8), with the largest increase observed among children aged 0-4 years.(¶) During December 2021, the monthly hospitalization rate among unvaccinated adolescents aged 12-17 years (23.5) was six times that among fully vaccinated adolescents (3.8). Strategies to prevent COVID-19 among children and adolescents, including vaccination of eligible persons, are critical.*.

BACKGROUND: Pregnant women may be at increased risk for severe influenza-associated outcomes. OBJECTIVE: To describe characteristics and outcomes of hospitalized pregnant women with influenza. DESIGN: Repeated cross-sectional study. SETTING: The population-based U.S. Influenza Hospitalization Surveillance Network during the 2010-2011 through 2018-2019 influenza seasons. PATIENTS: Pregnant women (aged 15 to 44 years) hospitalized with laboratory-confirmed influenza identified through provider-initiated or facility-based testing practices. MEASUREMENTS: Clinical characteristics, interventions, and in-hospital maternal and fetal outcomes were obtained through medical chart abstraction. Multivariable logistic regression was used to evaluate the association between influenza A subtype and severe maternal influenza-associated outcomes, including intensive care unit (ICU) admission, mechanical ventilation, extracorporeal membrane oxygenation, or in-hospital death. RESULTS: Of 9652 women aged 15 to 44 years and hospitalized with influenza, 2690 (27.9%) were pregnant. Among the 2690 pregnant women, the median age was 28 years, 62% were in their third trimester, and 42% had at least 1 underlying condition. Overall, 32% were vaccinated against influenza and 88% received antiviral treatment. Five percent required ICU admission, 2% required mechanical ventilation, and 0.3% (n = 8) died. Pregnant women with influenza A H1N1 were more likely to have severe outcomes than those with influenza A H3N2 (adjusted risk ratio, 1.9 [95% CI, 1.3 to 2.8]). Most women (71%) were still pregnant at hospital discharge. Among 754 women who were no longer pregnant at discharge, 96% had a pregnancy resulting in live birth, and 3% experienced fetal loss. LIMITATION: Maternal and fetal outcomes that occurred after hospital discharge were not captured. CONCLUSION: Over 9 influenza seasons, one third of reproductive-aged women hospitalized with influenza were pregnant. Influenza A H1N1 was associated with more severe maternal outcomes. Pregnant women remain a high-priority target group for vaccination. PRIMARY FUNDING SOURCE: Centers for Disease Control and Prevention.

BACKGROUND: Antiviral treatment is recommended for hospitalized patients with suspected and confirmed influenza, but evidence is limited among children. We evaluated the effect of antiviral treatment on hospital length of stay (LOS) among children hospitalized with influenza. METHODS: We included children <18 years hospitalized with laboratory-confirmed influenza in the US Influenza Hospitalization Surveillance Network. We collected data for 2 cohorts: 1 with underlying medical conditions not admitted to the ICU (n = 309, 2012-2013) and an ICU cohort (including children with and without underlying conditions; n = 299, 2010-2011 to 2012-2013). We used a Cox model with antiviral receipt as a time-dependent variable to estimate hazard of discharge and a Kaplan-Meier survival analysis to determine LOS. RESULTS: Compared with those not receiving antiviral agents, LOS was shorter for those treated ≤2 days after illness onset in both the medical conditions (adjusted hazard ratio: 1.37, P = .02) and ICU (adjusted hazard ratio: 1.46, P = .007) cohorts, corresponding to 37% and 46% increases in daily discharge probability, respectively. Treatment ≥3 days after illness onset had no significant effect in either cohort. In the medical conditions cohort, median LOS was 3 days for those not treated versus 2 days for those treated ≤2 days after symptom onset (P = .005). CONCLUSIONS: Early antiviral treatment was associated with significantly shorter hospitalizations in children with laboratory-confirmed influenza and high-risk medical conditions or children treated in the ICU. These results support Centers for Disease Control and Prevention recommendations for prompt empiric antiviral treatment in hospitalized patients with suspected or confirmed influenza.

BACKGROUND: The COVID-19 pandemic has caused substantial morbidity and mortality. OBJECTIVE: To describe monthly clinical trends among adults hospitalized with COVID-19. DESIGN: Pooled cross-sectional study. SETTING: 99 counties in 14 states participating in the Coronavirus Disease 2019-Associated Hospitalization Surveillance Network (COVID-NET). PATIENTS: U.S. adults (aged ≥18 years) hospitalized with laboratory-confirmed COVID-19 during 1 March to 31 December 2020. MEASUREMENTS: Monthly hospitalizations, intensive care unit (ICU) admissions, and in-hospital death rates per 100 000 persons in the population; monthly trends in weighted percentages of interventions, including ICU admission, mechanical ventilation, and vasopressor use, among an age- and site-stratified random sample of hospitalized case patients. RESULTS: Among 116 743 hospitalized adults with COVID-19, the median age was 62 years, 50.7% were male, and 40.8% were non-Hispanic White. Monthly rates of hospitalization (105.3 per 100 000 persons), ICU admission (20.2 per 100 000 persons), and death (11.7 per 100 000 persons) peaked during December 2020. Rates of all 3 outcomes were highest among adults aged 65 years or older, males, and Hispanic or non-Hispanic Black persons. Among 18 508 sampled hospitalized adults, use of remdesivir and systemic corticosteroids increased from 1.7% and 18.9%, respectively, in March to 53.8% and 74.2%, respectively, in December. Frequency of ICU admission, mechanical ventilation, and vasopressor use decreased from March (37.8%, 27.8%, and 22.7%, respectively) to December (20.5%, 12.3%, and 12.8%, respectively); use of noninvasive respiratory support increased from March to December. LIMITATION: COVID-NET covers approximately 10% of the U.S. population; findings may not be generalizable to the entire country. CONCLUSION: Rates of COVID-19-associated hospitalization, ICU admission, and death were highest in December 2020, corresponding with the third peak of the U.S. pandemic. The frequency of intensive interventions for management of hospitalized patients decreased over time. These data provide a longitudinal assessment of clinical trends among adults hospitalized with COVID-19 before widespread implementation of COVID-19 vaccines. PRIMARY FUNDING SOURCE: Centers for Disease Control and Prevention.

Most COVID-19-associated hospitalizations occur in older adults, but severe disease that requires hospitalization occurs in all age groups, including adolescents aged 12-17 years (1). On May 10, 2021, the Food and Drug Administration expanded the Emergency Use Authorization for Pfizer-BioNTech COVID-19 vaccine to include persons aged 12-15 years, and CDC's Advisory Committee on Immunization Practices recommended it for this age group on May 12, 2021.* Before that time, COVID-19 vaccines had been available only to persons aged ≥16 years. Understanding and describing the epidemiology of COVID-19-associated hospitalizations in adolescents and comparing it with adolescent hospitalizations associated with other vaccine-preventable respiratory viruses, such as influenza, offers evidence of the benefits of expanding the recommended age range for vaccination and provides a baseline and context from which to assess vaccination impact. Using the Coronavirus Disease 2019-Associated Hospitalization Surveillance Network (COVID-NET), CDC examined COVID-19-associated hospitalizations among adolescents aged 12-17 years, including demographic and clinical characteristics of adolescents admitted during January 1-March 31, 2021, and hospitalization rates (hospitalizations per 100,000 persons) among adolescents during March 1, 2020-April 24, 2021. Among 204 adolescents who were likely hospitalized primarily for COVID-19 during January 1-March 31, 2021, 31.4% were admitted to an intensive care unit (ICU), and 4.9% required invasive mechanical ventilation; there were no associated deaths. During March 1, 2020-April 24, 2021, weekly adolescent hospitalization rates peaked at 2.1 per 100,000 in early January 2021, declined to 0.6 in mid-March, and then rose to 1.3 in April. Cumulative COVID-19-associated hospitalization rates during October 1, 2020-April 24, 2021, were 2.5-3.0 times higher than were influenza-associated hospitalization rates from three recent influenza seasons (2017-18, 2018-19, and 2019-20) obtained from the Influenza Hospitalization Surveillance Network (FluSurv-NET). Recent increased COVID-19-associated hospitalization rates in March and April 2021 and the potential for severe disease in adolescents reinforce the importance of continued COVID-19 prevention measures, including vaccination and correct and consistent wearing of masks by persons not yet fully vaccinated or when required by laws, rules, or regulations.(†).

BACKGROUND: Respiratory syncytial virus (RSV) infection causes substantial morbidity and mortality in children and adults. Socioeconomic status (SES) is known to influence many health outcomes, but there have been few studies of the relationship between RSV-associated illness and SES, particularly in adults. Understanding this association is important in order to identify and address disparities and to prioritize resources for prevention. METHODS: Adults hospitalized with a laboratory-confirmed RSV infection were identified through population-based surveillance at multiple sites in the U.S. The incidence of RSV-associated hospitalizations was calculated by census-tract (CT) poverty and crowding, adjusted for age. Log binomial regression was used to evaluate the association between Intensive Care Unit (ICU) admission or death and CT poverty and crowding. RESULTS: Among the 1713 cases, RSV-associated hospitalization correlated with increased CT level poverty and crowding. The incidence rate of RSV-associated hospitalization was 2.58 (CI 2.23, 2.98) times higher in CTs with the highest as compared to the lowest percentages of individuals living below the poverty level (≥ 20 and < 5%, respectively). The incidence rate of RSV-associated hospitalization was 1.52 (CI 1.33, 1.73) times higher in CTs with the highest as compared to the lowest levels of crowding (≥5 and < 1% of households with > 1 occupant/room, respectively). Neither CT level poverty nor crowding had a correlation with ICU admission or death. CONCLUSIONS: Poverty and crowding at CT level were associated with increased incidence of RSV-associated hospitalization, but not with more severe RSV disease. Efforts to reduce the incidence of RSV disease should consider SES.

Pregnant women might be at increased risk for severe coronavirus disease 2019 (COVID-19) (1,2). The COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) (3) collects data on hospitalized pregnant women with laboratory-confirmed SARS-CoV-2, the virus that causes COVID-19; to date, such data have been limited. During March 1-August 22, 2020, approximately one in four hospitalized women aged 15-49 years with COVID-19 was pregnant. Among 598 hospitalized pregnant women with COVID-19, 54.5% were asymptomatic at admission. Among 272 pregnant women with COVID-19 who were symptomatic at hospital admission, 16.2% were admitted to an intensive care unit (ICU), and 8.5% required invasive mechanical ventilation. During COVID-19-associated hospitalizations, 448 of 458 (97.8%) completed pregnancies resulted in a live birth and 10 (2.2%) resulted in a pregnancy loss. Testing policies based on the presence of symptoms might miss COVID-19 infections during pregnancy. Surveillance of pregnant women with COVID-19, including those with asymptomatic infections, is important to understand the short- and long-term consequences of COVID-19 for mothers and newborns. Identifying COVID-19 in women during birth hospitalizations is important to guide preventive measures to protect pregnant women, parents, newborns, other patients, and hospital personnel. Pregnant women and health care providers should be made aware of the potential risks for severe COVID-19 illness, adverse pregnancy outcomes, and ways to prevent infection.

Since SARS-CoV-2, the novel coronavirus that causes coronavirus disease 2019 (COVID-19), was first detected in December 2019 (1), approximately 1.3 million cases have been reported worldwide (2), including approximately 330,000 in the United States (3). To conduct population-based surveillance for laboratory-confirmed COVID-19-associated hospitalizations in the United States, the COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) was created using the existing infrastructure of the Influenza Hospitalization Surveillance Network (FluSurv-NET) (4) and the Respiratory Syncytial Virus Hospitalization Surveillance Network (RSV-NET). This report presents age-stratified COVID-19-associated hospitalization rates for patients admitted during March 1-28, 2020, and clinical data on patients admitted during March 1-30, 2020, the first month of U.S. surveillance. Among 1,482 patients hospitalized with COVID-19, 74.5% were aged >/=50 years, and 54.4% were male. The hospitalization rate among patients identified through COVID-NET during this 4-week period was 4.6 per 100,000 population. Rates were highest (13.8) among adults aged >/=65 years. Among 178 (12%) adult patients with data on underlying conditions as of March 30, 2020, 89.3% had one or more underlying conditions; the most common were hypertension (49.7%), obesity (48.3%), chronic lung disease (34.6%), diabetes mellitus (28.3%), and cardiovascular disease (27.8%). These findings suggest that older adults have elevated rates of COVID-19-associated hospitalization and the majority of persons hospitalized with COVID-19 have underlying medical conditions. These findings underscore the importance of preventive measures (e.g., social distancing, respiratory hygiene, and wearing face coverings in public settings where social distancing measures are difficult to maintain)(dagger) to protect older adults and persons with underlying medical conditions, as well as the general public. In addition, older adults and persons with serious underlying medical conditions should avoid contact with persons who are ill and immediately contact their health care provider(s) if they have symptoms consistent with COVID-19 (https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html) (5). Ongoing monitoring of hospitalization rates, clinical characteristics, and outcomes of hospitalized patients will be important to better understand the evolving epidemiology of COVID-19 in the United States and the clinical spectrum of disease, and to help guide planning and prioritization of health care system resources.

Importance: Seasonal influenza virus infection is a major cause of morbidity and mortality and may be associated with respiratory and nonrespiratory diagnoses. Objective: To examine the respiratory and nonrespiratory diagnoses reported for adults hospitalized with laboratory-confirmed influenza between 2010 and 2018 in the United States. Design, Setting, and Participants: This cross-sectional study used data from the US Influenza Hospitalization Surveillance Network (FluSurv-NET) from October 1 through April 30 of the 2010-2011 through 2017-2018 influenza seasons. FluSurv-NET is a population-based, multicenter surveillance network with a catchment area that represents approximately 9% of the US population. Patients are identified by practitioner-ordered influenza testing. Adults (aged >/=18 years) hospitalized with laboratory-confirmed influenza were included in the study. Exposures: FluSurv-NET defines laboratory-confirmed influenza as a positive influenza test result by rapid antigen assay, reverse transcription-polymerase chain reaction, direct or indirect fluorescent staining, or viral culture. Main Outcomes and Measures: Acute respiratory or nonrespiratory diagnoses were defined using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) and International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) discharge diagnosis codes. The analysis included calculation of the frequency of acute respiratory and nonrespiratory diagnoses with a descriptive analysis of patient demographic characteristics, underlying medical conditions, and in-hospital outcomes by respiratory and nonrespiratory diagnoses. Results: Of 89 999 adult patients hospitalized with laboratory-confirmed influenza, 76 649 (median age, 69 years; interquartile range, 55-82 years; 55% female) had full medical record abstraction and at least 1 ICD code for an acute diagnosis. In this study, 94.9% of patients had a respiratory diagnosis and 46.5% had a nonrespiratory diagnosis, including 5.1% with only nonrespiratory diagnoses. Pneumonia (36.3%), sepsis (23.3%), and acute kidney injury (20.2%) were the most common acute diagnoses. Fewer patients with only nonrespiratory diagnoses received antiviral therapy for influenza compared with those with respiratory diagnoses (81.4% vs 88.9%; P < .001). Conclusions and Relevance: Nonrespiratory diagnoses occurred frequently among adults hospitalized with influenza, further contributing to the burden of infection in the United States. The findings suggest that during the influenza season, practitioners should consider influenza in their differential diagnosis for patients who present to the hospital with less frequently recognized manifestations and initiate early antiviral treatment for patients with suspected or confirmed infection.

BACKGROUND: Hospitalized immunocompromised (IC) adults with influenza may have worse outcomes than hospitalized non-immunocompromised adults. METHODS: We identified adults (>/=18 years) hospitalized with laboratory-confirmed influenza during 2011-2015 seasons through CDC's Influenza Hospitalization Surveillance Network. IC patients had >/=1: HIV/AIDS, cancer, stem cell or organ transplantation, non-steroid immunosuppressive therapy, immunoglobulin deficiency, asplenia, or other rare conditions. We compared demographic and clinical characteristics of IC and non-IC adults using descriptive statistics and used multivariable logistic regression and Cox proportional hazards models to control for confounding by patient demographic characteristics, pre-existing medical conditions, influenza vaccination, and other factors. RESULTS: Among 35,348 adults, 3633 (10%) were IC; cancer (44%), non-steroid immunosuppressive therapy (44%), and HIV (17%) were most common. IC patients were more likely than non-IC patients to have received influenza vaccination (53% vs. 46%; p<0.001), and ~85% of both groups received antivirals. In multivariable analysis, IC adults had higher mortality (adjusted odds ratio (aOR) [95% confidence interval (CI)]: 1.46 [1.20-1.76]). Intensive care was more likely among IC patients 65-79 years (aOR [95% CI]: 1.25 [1.06-1.48]) and >80 years (aOR [95% CI]: 1.35 [1.06-1.73]) compared with non-IC patients in those age groups. IC patients were hospitalized longer (adjusted hazard ratio of discharge [95% CI]: 0.86 [0.83-0.88]) and were more likely to require mechanical ventilation (aOR [95% CI] 1.19 [1.05-1.36]). CONCLUSIONS: Substantial morbidity and mortality occurred among IC adults hospitalized with influenza. Influenza vaccination and antiviral administration could be increased in both IC and non-IC adults.