BACKGROUND: Young children are at increased risk of severe outcomes from influenza illness, including hospitalization. We conducted a case-control study to identify risk factors for influenza-associated hospitalizations among children in U.S. Emerging Infections Program sites. METHODS: Cases were children 6-59 months of age hospitalized for laboratory-confirmed influenza infections during 2005-08. Age- and zip-code-matched controls were enrolled. Data on child, caregiver, and household characteristics were collected from parents and medical records. Conditional logistic regression was used to identify independent risk factors for hospitalization. RESULTS: We enrolled 290 (64%) of 454 eligible cases and 1,089 (49%) of 2,204 eligible controls. Risk for influenza hospitalization increased with maternal age <26 years (odds ratio [OR] 1.8, 95% confidence interval [CI] 1.1-2.9); household income below the poverty threshold (OR 2.2, CI 1.4-3.6); smoking by >50% of household members (OR 2.9, CI 1.4-6.6); lack of household influenza vaccination (OR 1.8, CI 1.2-2.5); and presence of chronic illnesses, including hematologic/oncologic (OR 11.8, CI 4.5-31.0), pulmonary (OR 2.9, CI 1.9-4.4), and neurologic (OR 3.8, CI 1.6-9.2) conditions. Full influenza immunization decreased the risk among children aged 6-23 months (OR 0.5, CI 0.3-0.9) but not among those 24-59 months of age (OR 1.5, CI 0.8-3.0; p-value for difference = 0.01). CONCLUSIONS: Chronic illnesses, young maternal age, poverty, household smoking, and lack of household influenza vaccination increased the risk of influenza hospitalization. These characteristics may help providers to identify young children who are at greatest risk for severe outcomes from influenza illness.

Nineteen patients with oseltamivir-resistant seasonal influenza A (H1N1) infections were randomized to receive oseltamivir or placebo. Nasopharyngeal swabs were obtained, and clinical and virologic outcomes were compared, stratified by early or late treatment. Neuraminidase inhibition assay and pyrosequencing for H275Y confirmed resistance. Twelve (63%) patients received oseltamivir; 8 (67%) received late treatment. Seven (37%) patients received placebo; 6 (86%) presented >48 hours after onset. Time to 50% decrease in symptom severity, complete symptom resolution, and first negative culture were shortest among the early treatment group. While sample size prohibits a strong conclusion, future studies should evaluate for similar trends. (Please cite this paper as: Dharan et al. (2011) Clinical and virologic outcomes in patients with oseltamivir-resistant seasonal influenza A (H1N1) infections: results from a clinical trial. Influenza and Other Respiratory Viruses DOI: 10.1111/j.1750-2659.2011.00312.x).

INTRODUCTION: In December 2008, new interim guidelines on the use of influenza antiviral agents were released in response to a high prevalence of circulating oseltamivir-resistant seasonal influenza A(H1N1) and adamantane-resistant influenza A(H3N2) viruses. Zanamivir, oseltamivir +/- an adamantane, or oseltamivir was recommended, depending on virus type, subtype, and local surveillance data. MATERIALS AND METHODS: Information about antiviral prescribing practices among IDSA Emerging Infections Network (EIN) members was obtained using two web-based questionnaires; one in January 2009 regarding the prior 2007-08 influenza season and one in April 2009 (prepandemic), regarding the concurrent 2008-09 season. RESULTS: In the 2007-08 survey, 646 (52%) of 1249 EIN members responded and in the 2008-09 season survey, 350 (27%) of 1281 responded. In 2008-09 vs. 2007-08: 59% vs. 69% prescribed or recommended antivirals for treatment (p<.0001); 48% vs. 80% prescribed oseltamivir alone and 39% vs. 10% prescribed zanamivir alone (p<.0001 for both). During 2008-09 28% reported treating fewer patients compared with 2007-08; 42% felt antivirals were less effective due to resistance and 40% felt patients had less severe illness. During 2008-09, 42% of respondents reported difficulty providing zanamivir to patients vs. 5% for oseltamivir (p<.0001). Only 11% of respondents could test for influenza A subtype. During both seasons, approximately 55% used local surveillance data to make treatment decisions. DISCUSSION: A mild winter influenza season, difficulty obtaining recommended agents, and lack of access to subtype diagnosis and surveillance data may have contributed to reduced antiviral use during 2008-2009.

During the 2007–2008 influenza season, we collected epidemiologic and clinical information from patients infected with seasonal influenza A (H1N1) viruses to describe the characteristics of oseltamivir-resistant infection and compare them with the characteristics of oseltamivir-susceptible infection [1]. Here we use the data collected to compare the clinical symptoms and outcomes of patients with oseltamivir-resistant and oseltamivir-susceptible A (H1N1) virus infections that were treated and not treated with antiviral agents. Specimens for laboratory testing were collected before antivirals were started. Few reports that correlate antiviral resistance, determined by in vitro assays [2], with clinical response have been published [3]. | We used generalized estimating equations controlling for state as a clustered variable and age group, and we used Wilcoxon rank-sum tests for continuous var-iables. Among 99 patients with oselta-mivir-resistant A (H1N1) infection, 47 (47%) were treated; 44 (94%) received oseltamivir alone and 3 (6%) received oseltamivir and rimantadine. Among 182 patients with oseltamivir-susceptible A (H1N1) infections, 64 (35%) were treated; 60 (94%) received oseltamivir, 2 (3%) received amantadine, 1 (2%) received rimantadine, and 1 (2%) received zanamivir. We excluded 37 case patients: 14 who were <1 year old, 2 who died before a decision on antiviral treatment could have been made, 3 who were treated with oseltamivir and an adamantane, and 19 for whom antiviral treatment could not be confirmed.

In 2006, national influenza surveillance was implemented in Vietnam. Epidemiologic and demographic data and a throat swab for influenza testing were collected from a subset of outpatients with influenza-like illness (ILI). During January 1, 2006 through December 31, 2007, of 184,521 ILI cases identified at surveillance sites, 11,082 were tested and 2112 (19%) were positive for influenza by reverse transcription polymerase chain reaction. Influenza viruses were detected year-round, and similar peaks in influenza activity were observed in all surveillance regions, coinciding with cooler and rainy periods. Studies are needed to ascertain the disease burden and impact of influenza in Vietnam.

An outbreak of oseltamivir-resistant influenza A (H1N1) occurred in a long-term care facility. Eight (47%) of 17 and 1 (6%) of 16 residents in 2 wards had oseltamivir-resistant influenza A virus (H1N1) infections. Initial outbreak response included treatment and prophylaxis with oseltamivir. The outbreak abated, likely because of infection control measures.