Epidemiology of 2009 pandemic influenza A (H1N1) deaths in the United States, April-July 2009.

During the spring of 2009, pandemic influenza A (H1N1) virus (pH1N1) was recognized and rapidly spread worldwide. To describe the geographic distribution and patient characteristics of pH1N1-associated deaths in the United States, the Centers for Disease Control and Prevention requested information from health departments on all laboratory-confirmed pH1N1 deaths reported from 17 April through 23 July 2009. Data were collected using medical charts, medical examiner reports, and death certificates. A total of 377 pH1N1-associated deaths were identified, for a mortality rate of .12 deaths per 100,000 population. Activity was geographically localized, with the highest mortality rates in Hawaii, New York, and Utah. Seventy-six percent of deaths occurred in persons aged 18-65 years, and 9% occurred in persons aged ≥ 65 years. Underlying medical conditions were reported for 78% of deaths: chronic lung disease among adults (39%) and neurologic disease among children (54%). Overall mortality associated with pH1N1 was low; however, the majority of deaths occurred in persons aged <65 years with underlying medical conditions.

Infections with oseltamivir-resistant influenza A(H1N1) virus in the United States.

CONTEXT: During the 2007-2008 influenza season, oseltamivir resistance among influenza A(H1N1) viruses increased significantly for the first time worldwide. Early surveillance data suggest that the prevalence of oseltamivir resistance among A(H1N1) viruses will most likely be higher during the 2008-2009 season. OBJECTIVES: To describe patients infected with oseltamivir-resistant influenza A(H1N1) virus and to determine whether there were any differences between these patients and patients infected with oseltamivir-susceptible A(H1N1) virus in demographic or epidemiological characteristics, clinical symptoms, severity of illness, or clinical outcomes. DESIGN, SETTING, AND PATIENTS: Influenza A(H1N1) viruses that were identified and submitted to the Centers for Disease Control and Prevention by US public health laboratories between September 30, 2007, and May 17, 2008, and between September 28, 2008, and February 19, 2009, were tested as part of ongoing surveillance. Oseltamivir resistance was determined by neuraminidase inhibition assay and pyrosequencing analysis. Information was collected using a standardized case form from patients with oseltamivir-resistant A(H1N1) infections and a comparison group of patients with oseltamivir-susceptible A(H1N1) infections during 2007-2008. MAIN OUTCOME MEASURES: Demographic and epidemiological information as well as clinical information, including symptoms, severity of illness, and clinical outcomes. RESULTS: During the 2007-2008 season, influenza A(H1N1) accounted for an estimated 19% of circulating influenza viruses in the United States. Among 1155 influenza A(H1N1) viruses tested from 45 states, 142 (12.3%) from 24 states were resistant to oseltamivir. Data were available for 99 oseltamivir-resistant cases and 182 oseltamivir-susceptible cases from this period. Among resistant cases, median age was 19 years (range, 1 month to 62 years), 5 patients (5%) were hospitalized, and 4 patients (4%) died. None reported oseltamivir exposure before influenza diagnostic sample collection. No significant differences were found between cases of oseltamivir-resistant and oseltamivir-susceptible influenza in demographic characteristics, underlying medical illness, or clinical symptoms. Preliminary data from the 2008-2009 influenza season identified resistance to oseltamivir among 264 of 268 influenza A(H1N1) viruses (98.5%) tested. CONCLUSIONS: Oseltamivir-resistant A(H1N1) viruses circulated widely in the United States during the 2007-2008 influenza season, appeared to be unrelated to oseltamivir use, and appeared to cause illness similar to oseltamivir-susceptible A(H1N1) viruses. Circulation of oseltamivir-resistant A(H1N1) viruses will continue, with a higher prevalence of resistance, during the 2008-2009 season.