Fever is not considered a typical presentation of pertussis. We characterized fever among 7840 pertussis cases from the Centers for Disease Control and Prevention's Enhanced Pertussis Surveillance with cough onset from 2015 to 2022. Ten percent of cases had a reported fever. The presence of fever should not rule out pertussis as a cause of cough illness.

The invasion of Anopheles stephensi in Africa warrants investigation of neighboring countries. In this study, genetic analysis was applied to determine the status of An. stephensi in southern Yemen. Cytochrome c oxidase subunit I (COI) and internal transcribed spacer 2 (ITS2) were sequenced in An. stephensi collected in Dar Sa'ad (Aden City), Tuban, Rodoom, Al Mukalla, and Sayhut, and phylogenetic analysis confirmed An. stephensi identity. Our analyses revealed that the ITS2 sequences were identical in all An. stephensi, while COI analysis revealed two haplotypes, one previously reported in northern Horn of Africa and one identified in this study for the first time. Overall, these findings revealed low levels of mitochondrial DNA diversity, which is consistent with a more recent population introduction in parts of southern Yemen relative to the Horn of Africa. Further, whole genomic analysis is needed to elucidate the original connection with invasive populations of An. stephensi in the Horn of Africa.

CONTEXT: The first case of mpox was detected in the United States in a Laboratory Response Network (LRN) laboratory at the Massachusetts Department of Public Health on May 17, 2022. Through previous years of smallpox preparedness efforts by the United States government, testing capacity in LRN laboratories across the United States utilizing the FDA-cleared Centers for Disease Control and Prevention (CDC) Non-variola orthopoxvirus (NVO) test was approximately 6000 tests weekly across the nation prior to the mpox outbreak. By early June 2022, the LRN laboratories had capacity to perform up to 8000 tests per week. As the outbreak expanded, cases were identified in every United States state, peaking at ~3000 cases per week nationally in August 2022. OBJECTIVE: Although NVO testing capacity in LRN laboratories exceeded national mpox testing demand overall, LRN testing access in some areas was challenged and test expansion was necessary. PARTICIPANTS: CDC engaged with partners and select commercial laboratories early to increase diagnostic testing access by allowing these commercial laboratories to utilize the NVO test. SETTING: The expansion of testing to commercial laboratories increased testing availability, capacity, and volume nationwide. This was the first time that CDC shared an FDA 510k-cleared molecular test with commercial laboratories to support a public health emergency. DESIGN: Extensive efforts were made to ensure the CDC NVO test was used appropriately in the private sector and that the transfer process met regulatory requirements. MAIN OUTCOME MEASURES, RESULTS, CONCLUSIONS: These novel methods to expand NVO testing to commercial laboratories increased national testing capacity to 80 000 mpox tests/week. Test volumes among these laboratories never exceeded this expanded capacity. The rapid increase in the nation's testing capacity, in conjunction and coordination with other public and private health efforts, helped to detect cases rapidly. These actions demonstrated the importance of highly functional and efficient public health and private sector partnerships for responding to public health emergencies.

OBJECTIVES: The Laboratory Response Network (LRN) consists of US and international laboratories that respond to public health emergencies, such as biothreats. We used a qualitative approach to assess the successes and challenges of the LRN during the initial 10 weeks of the 2022 mpox outbreak (May 17-July 31, 2022). METHODS: We conducted 9 unstructured interviews, which included 3 interviews with subject matter experts from the Centers for Disease Control and Prevention (CDC) and 6 interviews with state and local public health laboratories and epidemiologists and Association of Public Health Laboratories (APHL) staff. We asked guiding questions on investments in preparedness, successes, and challenges during the initial mpox response and asked for suggestions to improve future LRN responses to infectious disease outbreaks. We also reviewed data from 2 contemporaneous APHL surveys conducted in June and July 2022 in 84 LRN public health laboratories. RESULTS: Notable successes included availability of an assay that had received clearance from the US Food and Drug Administration (FDA) for testing orthopoxviruses (non-variola Orthopoxvirus [NVO] assay) and a trained workforce; strong relationships among FDA, CDC, and the LRN; and strong communications between LRN laboratories and CDC. Challenges included variability among LRN laboratories in self-reported testing capacity, barriers to accessing the NVO assay for health care providers, and gaps in LRN function during surges of testing needs. CONCLUSIONS: The LRN system plays an essential role in the response to emerging infectious disease outbreaks in the United States. Lessons learned from the LRN's initial response to the mpox outbreak can help guide improvements to better position the LRN for future responses, including continued engagement with health care providers, commercial laboratories, and laboratories in health care settings.

BACKGROUND: In 2020, the Council of State and Territorial Epidemiologists (CSTE) pertussis case definition was modified; the main change was classifying PCR-positive cases as confirmed, regardless of cough duration. Pertussis data reported through Enhanced Pertussis Surveillance (EPS) in seven sites and the National Notifiable Diseases Surveillance System (NNDSS) were used to evaluate the impact of the new case definition. METHODS: We compared the number of EPS cases with cough onset in 2020 to the number that would have been reported based on the prior (2014) CSTE case definition. To assess the impact of the change nationally, the proportion of EPS cases newly reportable under the 2020 CSTE case definition was applied to 2020 NNDSS data to estimate how many additional cases were captured nationally. RESULTS: Among 442 confirmed and probable cases reported to EPS states in 2020, 42 (9.5%) were newly reportable according to the 2020 case definition. Applying this proportion to the 6,124 confirmed and probable cases reported nationally in 2020, we estimated that the new definition added 582 cases. Had the case definition not changed, reported cases in 2020 would have decreased by 70% from 2019; the observed decrease was 67%. CONCLUSIONS: Despite a substantial decrease in reported pertussis cases in the setting of COVID-19, our data show that the 2020 pertussis case definition change resulted in additional case reporting compared with the previous case definition, providing greater opportunities for public health interventions such as prophylaxis of close contacts.

Updated (bivalent) COVID-19 vaccines were first recommended by CDC on September 1, 2022.* An analysis of case and death rates by vaccination status shortly after authorization of bivalent COVID-19 vaccines showed that receipt of a bivalent booster dose provided additional protection against SARS-CoV-2 infection and associated death (1). In this follow-up report on the durability of bivalent booster protection against death among adults aged ≥65 years, mortality rate ratios (RRs) were estimated among unvaccinated persons and those who received a bivalent booster dose by time since vaccination during three periods of Omicron lineage predominance (BA.5 [September 18–November 5, 2022], BQ.1/BQ.1.1 [November 6, 2022–January 21, 2023], and XBB.1.5 [January 22–April 1, 2023]).† | | During September 18, 2022–April 1, 2023, weekly counts of COVID-19–associated deaths§ among unvaccinated persons and those who received a bivalent booster dose¶ were reported from 20 U.S. jurisdictions** that routinely link case surveillance data to immunization registries and vital registration databases (1). Vaccinated persons who did not receive a bivalent COVID-19 booster dose were excluded. Rate denominators were calculated from vaccine administration data and 2019 U.S. intercensal population estimates,†† with numbers of unvaccinated persons estimated by subtracting numbers of vaccinated persons from the 2019 intercensal population estimates, as previously described§§ (1). Average weekly mortality rates were estimated based on date of specimen collection¶¶ during each variant period by vaccination status and time since bivalent booster dose receipt. RRs were calculated by dividing rates among unvaccinated persons by rates among bivalent booster dose recipients; after detrending the underlying linear changes in weekly rates, 95% CIs were estimated from the remaining variation in rates observed*** (1). SAS (version 9.4; SAS Institute) and R (version 4.1.2; R Foundation) software were used to conduct all analyses. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.†††

As part of public health preparedness for infectious disease threats, CDC collaborates with other U.S. public health officials to ensure that the Laboratory Response Network (LRN) has diagnostic tools to detect Orthopoxviruses, the genus that includes Variola virus, the causative agent of smallpox. LRN is a network of state and local public health, federal, U.S. Department of Defense (DOD), veterinary, food, and environmental testing laboratories. CDC developed, and the Food and Drug Administration (FDA) granted 510(k) clearance* for the Non-variola Orthopoxvirus Real-time PCR Primer and Probe Set (non-variola Orthopoxvirus [NVO] assay), a polymerase chain reaction (PCR) diagnostic test to detect NVO. On May 17, 2022, CDC was contacted by the Massachusetts Department of Public Health (DPH) regarding a suspected case of monkeypox, a disease caused by the Orthopoxvirus Monkeypox virus. Specimens were collected and tested by the Massachusetts DPH public health laboratory with LRN testing capability using the NVO assay. Nationwide, 68 LRN laboratories had capacity to test approximately 8,000 NVO tests per week during June. During May 17-June 30, LRN laboratories tested 2,009 specimens from suspected monkeypox cases. Among those, 730 (36.3%) specimens from 395 patients were positive for NVO. NVO-positive specimens from 159 persons were confirmed by CDC to be monkeypox; final characterization is pending for 236. Prompt identification of persons with infection allowed rapid response to the outbreak, including isolation and treatment of patients, administration of vaccines, and other public health action. To further facilitate access to testing and increase convenience for providers and patients by using existing provider-laboratory relationships, CDC and LRN are supporting five large commercial laboratories with a national footprint (Aegis Science, LabCorp, Mayo Clinic Laboratories, Quest Diagnostics, and Sonic Healthcare) to establish NVO testing capacity of 10,000 specimens per week per laboratory. On July 6, 2022, the first commercial laboratory began accepting specimens for NVO testing based on clinician orders.

The Somali Region of Ethiopia has been affected by drought for several years. Drought conditions have led to food and water scarcity and a humanitarian crisis in the region. In January 2017, an outbreak of acute watery diarrhea (AWD) was declared in the region. AWD prevention and control activities include strengthening water, sanitation, and hygiene (WASH) services. Access to safe drinking water is critical in preventing transmission of AWD and chlorine is an effective chemical to disinfect water supplies. The US Centers for Disease Control and Prevention collaborated with the WASH Cluster and the United Nations Children’s Fund, Ethiopia, to provide technical assistance to the Somali Regional Water Bureau to improve chlorination of drinking water supplies and quickly assess water quality improvements in Jijiga town, Fafan Zone. Timely sharing of surveillance and case investigation data allowed for the identification of gaps within the water supply system in Jijiga and implementation of centralized and decentralized chlorination interventions and monitoring systems. Pilot use of a rapid assessment to determine residual chlorine levels at various points in the city helped improve chlorination intervention impact. This work illustrates that rapid community-level water quality improvements can be implemented and assessed quickly to improve interventions during outbreaks.

Coronavirus disease 2019 (COVID-19) is a viral respiratory illness caused by SARS-CoV-2. During January 21-July 25, 2020, in response to official requests for assistance with COVID-19 emergency public health response activities, CDC deployed 208 teams to assist 55 state, tribal, local, and territorial health departments. CDC deployment data were analyzed to summarize activities by deployed CDC teams in assisting state, tribal, local, and territorial health departments to identify and implement measures to contain SARS-CoV-2 transmission (1). Deployed teams assisted with the investigation of transmission in high-risk congregate settings, such as long-term care facilities (53 deployments; 26% of total), food processing facilities (24; 12%), correctional facilities (12; 6%), and settings that provide services to persons experiencing homelessness (10; 5%). Among the 208 deployed teams, 178 (85%) provided assistance to state health departments, 12 (6%) to tribal health departments, 10 (5%) to local health departments, and eight (4%) to territorial health departments. CDC collaborations with health departments have strengthened local capacity and provided outbreak response support. Collaborations focused attention on health equity issues among disproportionately affected populations (e.g., racial and ethnic minority populations, essential frontline workers, and persons experiencing homelessness) and through a place-based focus (e.g., persons living in rural or frontier areas). These collaborations also facilitated enhanced characterization of COVID-19 epidemiology, directly contributing to CDC data-informed guidance, including guidance for serial testing as a containment strategy in high-risk congregate settings, targeted interventions and prevention efforts among workers at food processing facilities, and social distancing.

The Laboratory Response Network (LRN) was established in 1999 to ensure an effective laboratory response to high-priority public health threats. The LRN for biological threats (LRN-B) provides a laboratory infrastructure to respond to emerging infectious diseases. Since 2012, the LRN-B has been involved in 3 emerging infectious disease outbreak responses. We evaluated the LRN-B role in these responses and identified areas for improvement. LRN-B laboratories tested 1097 specimens during the 2014 Middle East Respiratory Syndrome Coronavirus outbreak, 180 specimens during the 2014-2015 Ebola outbreak, and 92 686 specimens during the 2016-2017 Zika virus outbreak. During the 2014-2015 Ebola outbreak, the LRN-B uncovered important gaps in biosafety and biosecurity practices. During the 2016-2017 Zika outbreak, the LRN-B identified the data entry bottleneck as a hindrance to timely reporting of results. Addressing areas for improvement may help LRN-B reference laboratories improve the response to future public health emergencies.

BACKGROUND: Strengthening the quality of laboratory diagnostics is a key part of building global health capacity. In 2015, the Centers for Disease Control and Prevention (CDC), the Southeast European Center for Surveillance and Control of Infectious Diseases (SECID), WHO European Regional Office (WHO EURO) and American Public Health Laboratories (APHL) collaborated to address laboratory quality training needs in Southeast Europe. Together, they developed a quality assurance (QA) mentorship program for six national laboratories (Laboratories A-E) in five countries utilizing APHL international consultants. The primary goal of the mentorship program was to help laboratories become recognized by WHO as National Influenza Centers (NICs). The program aimed to do this by strengthening influenza laboratory capacity by implementing quality management systems (QMS) action steps. After 1 year, we evaluated participants' progress by the proportion of QMS action steps they had successfully implemented, as well as the value of mentorship as perceived by laboratory mentees, mentors, and primary program stakeholders from SECID and WHO EURO. METHODS: To understand perceived value we used the qualitative method of semi-structured interviews, applying grounded theory to the thematic analysis. RESULTS: Mentees showed clear progress, having completed 32 to 68% [median: 62%] of planned QMS action steps in their laboratories. In regards to the perceived value of the program, we found strong evidence that laboratory mentorship enhances laboratory quality improvement by promoting accountability to QMS implementation, raising awareness of the importance of QMS, and fostering collaborative problem solving. CONCLUSION: In conclusion, we found that significant accomplishments can be achieved when QA programs provide dedicated technical mentorship for QMS implementation. Since the start of the mentoring, Laboratory "B" has achieved NIC recognition by WHO, while two other labs made substantial progress and are scheduled for recognition in 2018. In the future, we recommend that mentorship is more inclusive of laboratory directors, and that programs evaluate the amount of staff time needed for mentorship activities, including lab-based assessments and mentoring.

Influenza virologic surveillance is critical each season for tracking influenza circulation, following trends in antiviral drug resistance, detecting novel influenza infections in humans, and selecting viruses for use in annual seasonal vaccine production. We developed a framework and process map for characterizing the landscape of US influenza virologic surveillance into 5 tiers of influenza testing: outpatient settings (tier 1), inpatient settings and commercial laboratories (tier 2), state public health laboratories (tier 3), National Influenza Reference Center laboratories (tier 4), and Centers for Disease Control and Prevention laboratories (tier 5). During the 2015-16 season, the numbers of influenza tests directly contributing to virologic surveillance were 804,000 in tiers 1 and 2; 78,000 in tier 3; 2,800 in tier 4; and 3,400 in tier 5. With the release of the 2017 US Pandemic Influenza Plan, the proposed framework will support public health officials in modeling, surveillance, and pandemic planning and response.

BACKGROUND: To collect information, identify training needs, and assist with influenza capacity building voluntary laboratory capacity assessments were conducted using a standardized tool in CDC cooperative agreement countries. To understand the usefulness of comparing results from repeat assessments and to determine if targeted training supported improvements, this paper details comparison of assessment results of conducting 17 repeat laboratory assessments between 2009 and 2013. METHODS: Laboratory assessments were conducted by SMEs in 17 laboratories (16 countries). We reviewed the quantitative assessment results of the laboratories that conducted both an initial and follow up assessment between 2009 to 2013 using repeated measures of Anova, (Mixed procedure of SAS (9.3)). Additionally, we compared the overall summary scores and the assessor recommendations from the two assessments. RESULTS: We were able to document a statistically significant improvement between the first and second assessments both on an aggregate as well as individual indicator score. Within the international capacity tool three of the eight categories recorded statistically significant improvement (equipment, management, and QA/QC), while the other tool categories (molecular, NIC, specimen, safety and virology) showed improvement in scores although not statistically significant. CONCLUSIONS: We found that using a standardized tool and quantitative framework is useful for documenting capacity and performance improvement in identified areas over time. The use of the tool and standard reports with assessor recommendations assisted laboratories with establishing, maintaining, and improving influenza laboratory practices. On-going assessments and the consistent application of the analytic framework over time will continue to aid in building a measurement knowledge base for laboratory capacity.

In January 2013, several months after Middle East respiratory syndrome coronavirus (MERS-CoV) was first identified in Saudi Arabia, Abu Dhabi, United Arab Emirates, began surveillance for MERS-CoV. We analyzed medical chart and laboratory data collected by the Health Authority-Abu Dhabi during January 2013-May 2014. Using real-time reverse transcription PCR, we tested respiratory tract samples for MERS-CoV and identified 65 case-patients. Of these patients, 23 (35%) were asymptomatic at the time of testing, and 4 (6%) showed positive test results for >3 weeks (1 had severe symptoms and 3 had mild symptoms). We also identified 6 clusters of MERS-CoV cases. This report highlights the potential for virus shedding by mildly ill and asymptomatic case-patients. These findings will be useful for MERS-CoV management and infection prevention strategies.

Middle East respiratory syndrome coronavirus (MERS-CoV) infections sharply increased in the Arabian Peninsula during spring 2014. In Abu Dhabi, United Arab Emirates, these infections occurred primarily among healthcare workers and patients. To identify and describe epidemiologic and clinical characteristics of persons with healthcare-associated infection, we reviewed laboratory-confirmed MERS-CoV cases reported to the Health Authority of Abu Dhabi during January 1, 2013-May 9, 2014. Of 65 case-patients identified with MERS-CoV infection, 27 (42%) had healthcare-associated cases. Epidemiologic and genetic sequencing findings suggest that 3 healthcare clusters of MERS-CoV infection occurred, including 1 that resulted in 20 infected persons in 1 hospital. MERS-CoV in healthcare settings spread predominantly before MERS-CoV infection was diagnosed, underscoring the importance of increasing awareness and infection control measures at first points of entry to healthcare facilities.

BACKGROUND: Monitoring influenza virus susceptibility to neuraminidase (NA) inhibitors (NAIs) is vital for detecting drug-resistant variants, and is primarily assessed using NA inhibition (NI) assays, supplemented by NA sequence analysis. However, differences in NI testing methodologies between surveillance laboratories results in variability of 50% inhibitory concentration (IC50) values, which impacts data sharing, reporting and interpretation. In 2011, the Centers for Disease Control and Prevention (CDC), in collaboration with the Association for Public Health Laboratories (APHL) spearheaded efforts to standardize fluorescence-based NI assay testing in the United States (U.S.), with the goal of achieving consistency of IC50 data. METHODS: For the standardization process, three participating state public health laboratories (PHLs), designated as National Surveillance Reference Centers for Influenza (NSRC-Is), assessed the NAI susceptibility of the 2011-12 CDC reference virus panel using stepwise procedures with support from the CDC reference laboratory. Next, the NSRC-Is assessed the NAI susceptibility of season 2011-12 U.S. influenza surveillance isolates (n=940), with a large subset (n=742) tested in parallel by CDC. Subsequently, U.S. influenza surveillance isolates (n=9629) circulating during the next three influenza seasons (2012-15), were independently tested by the three NSRC-Is (n=7331) and CDC (n=2298). RESULTS: The NI assay IC50s generated by respective NSRC-Is using viruses and drugs prepared by CDC were similar to those obtained with viruses and drugs prepared in-house, and were uniform between laboratories. IC50s for U.S. surveillance isolates tested during four consecutive influenza seasons (2011-15) were consistent from season to season, within and between laboratories. CONCLUSION: These results show that the NI assay is robust enough to be standardized, marking the first time IC50 data have been normalized across multiple laboratories, and used for U.S. national NAI susceptibility surveillance.

In this study, a multicenter evaluation of the Life Technologies TaqMan(R) Array Card (TAC) with 21 custom viral and bacterial respiratory assays was performed on the Applied Biosystems ViiA 7 Real-Time PCR System. The goal of the study was to demonstrate the analytical performance of this platform when compared to identical individual pathogen specific laboratory developed tests (LDTs) designed at the Centers for Disease Control and Prevention (CDC), equivalent LDTs provided by state public health laboratories, or to three different commercial multi-respiratory panels. CDC and Association of Public Health Laboratories (APHL) LDTs had similar analytical sensitivities for viral pathogens, while several of the bacterial pathogen APHL LDTs demonstrated sensitivities one log higher than the corresponding CDC LDT. When compared to CDC LDTs, TAC assays were generally one to two logs less sensitive depending on the site performing the analysis. Finally, TAC assays were generally more sensitive than their counterparts in three different commercial multi-respiratory panels. TAC technology allows users to spot customized assays and design TAC layout, simplify assay setup, conserve specimen, dramatically reduce contamination potential, and as demonstrated in this study, analyze multiple samples in parallel with good reproducibility between instruments and operators.

BACKGROUND: Laboratory testing is a fundamental component of influenza surveillance for detecting novel strains with pandemic potential and informing biannual vaccine strain selection. The United States (U.S.) Centers for Disease Control and Prevention (CDC), under the auspices of its WHO Collaborating Center for Influenza, is one of the major public health agencies which provides support globally to build national capacity for influenza surveillance. Our main objective was to determine if laboratory assessments supported capacity building efforts for improved global influenza surveillance. METHODS: In 2010, 35 national influenza laboratories were assessed in 34 countries, using a standardized tool. Post-assessment, each laboratory received a report with a list of recommendations for improvement. Uptake of recommendations were reviewed 3.2 mean years after the initial assessments and categorized as complete, in-progress, no action or no update. This was a retrospective study; follow-up took place through routine project management rather than at a set time-point post-assessment. WHO data on National Influenza Centre (NIC) designation, External Quality Assessment Project (EQAP) participation and FluNet reporting was used to measure laboratory capacity longitudinally and independently of the assessments. All data was further stratified by World Bank country income category. RESULTS: At follow-up, 81 % of 614 recommendations were either complete (350) or in-progress (145) for 32 laboratories (91 % response rate). The number of countries reporting to FluNet and the number of specimens they reported annually increased between 2005, when they were first funded by CDC, and 2010, the assessment year (p < 0.01). Improvements were also seen in EQAP participation and NIC designation over time and more so for low and lower-middle income countries. CONCLUSIONS: Assessments using a standardized tool have been beneficial to improving laboratory-based influenza surveillance. Specific recommendations helped countries identify and prioritize areas for improvement. Data from assessments helped CDC focus its technical assistance by country and region. Low and lower-middle income countries made greater improvements in their laboratories compared with upper-middle income countries. Future research could include an analysis of annual funding and technical assistance by country. Our approach serves as an example for capacity building for other diseases.

OBJECTIVES: The 2005 International Health Regulations (IHR 2005) emphasized the importance of laboratory capacity to detect emerging diseases including novel influenza viruses. To support IHR 2005 requirements and the need to enhance influenza laboratory surveillance capacity, the Association of Public Health Laboratories (APHL) and the Centers for Disease Control and Prevention (CDC) Influenza Division developed the International Influenza Laboratory Capacity Review (Tool). STUDY DESIGN: Data from 37 assessments were reviewed and analyzed to verify that the quantitative analysis results accurately depicted a laboratory's capacity and capabilities. METHODS: Subject matter experts in influenza and laboratory practice used an iterative approach to develop the Tool incorporating feedback and lessons learnt through piloting and implementation. To systematically analyze assessment data, a quantitative framework for analysis was added to the Tool. RESULTS: The review indicated that changes in scores consistently reflected enhanced or decreased capacity. The review process also validated the utility of adding a quantitative analysis component to the assessments and the benefit of establishing a baseline from which to compare future assessments in a standardized way. CONCLUSIONS: Use of the Tool has provided APHL, CDC and each assessed laboratory with a standardized analysis of the laboratory's capacity. The information generated is used to improve laboratory systems for laboratory testing and enhance influenza surveillance globally. We describe the development of the Tool and lessons learnt.

OBJECTIVE: To describe trends in hospitalizations with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection in New York City over 10 years and to explore the demographics and comorbidities of patients hospitalized with CA-MRSA infections. DESIGN: Retrospective analysis of hospital discharges from New York State's Statewide Planning and Research Cooperative System database from 1997 to 2006. PATIENTS: All patients greater than 1 year of age admitted to New York hospitals with diagnosis codes indicating MRSA who met the criteria for CA-MRSA on the basis of admission information and comorbidities. METHODS: We determined hospitalization rates and compared demographics and comorbidities of patients hospitalized with CA-MRSA versus those hospitalized with all other non-MRSA diagnoses by multivariable logistic regression. RESULTS: Of 18,226 hospitalizations with an MRSA diagnosis over 10 years, 3,579 (20%) were classified as community-associated. The CA-MRSA hospitalization rate increased from 1.47 to 10.65 per 100,000 people overall from 1997 to 2006. Relative to non-MRSA hospitalizations, men, children, Bronx and Manhattan residents, the homeless, patients with human immunodeficiency virus (HIV) infection, and persons with diabetes had higher adjusted odds of CA-MRSA hospitalization. CONCLUSIONS: The CA-MRSA hospitalization rate appeared to increase between 1997 and 2006 in New York City, with residents of the Bronx and Manhattan, men, and persons with HIV infection or diabetes at increased odds of hospitalization with CA-MRSA. Further studies are needed to explore how changes in MRSA incidence, access to care, and other factors may have impacted these rates.