Epidemiology of influenza A (H1N1)pdm09-associated deaths in the United States, September-October 2009.

ABSTRACT

BACKGROUND: From April to July 2009, the United States experienced a wave of influenza A (H1N1)pdm09 virus (H1N1pdm09) infection. The majority of the deaths during that period occurred in persons <65 years of age with underlying medical conditions. OBJECTIVE: To describe the epidemiology of H1N1pdm09-associated deaths in the US during the fall of 2009. METHODS: We collected demographic, medical history, and cause of death information on a nationally representative, stratified random sample of 323 H1N1pdm09-associated deaths that occurred during September 1-October 31, 2009. RESULTS: Data were available for 302/323 (93%) deaths. Most cases (74%) were 18-64 years of age and had ≥ 1 underlying medical condition (72%). Among cases aged <18 years, 16/43 (37%) had a chronic lung disease, and 15/43 (35%) a neurological disorder; among cases aged ≥ 18 years, 94/254 (37%) had a chronic lung disease and 84/254 (33%) had a metabolic disorder. The median number of days between symptom onset and death was six among children (range, 1-48) and 12 among adults (range, 0-109). Influenza antiviral agents were prescribed for 187/268 (70%) of cases, but only 48/153 (31%) received treatment within 2 days of illness onset. CONCLUSIONS: The characteristics of H1N1pdm09 deaths identified during the fall of 2009 were similar to those occurring April-July 2009. While most cases had conditions that were known to increase the risk for severe outcomes and were recommended to receive antiviral therapy, a minority of cases received antivirals early in the course of illness.