Influenza-like illness in the community during the emergence of 2009 pandemic influenza A(H1N1)--survey of 10 states, April 2009.

Following the emergence of 2009 pandemic influenza A(H1N1) virus (pH1N1) in the United States, the incidence of pH1N1 in the community was unclear, because not all persons with influenza come to medical attention. To better estimate the incidence of pH1N1 in the community early in the pandemic, a telephone survey was conducted in 10 states. The community incidence of influenza-like illness in April 2009 was 4.7 per 100 adults (95% confidence interval: 2.8-6.6); half of adults reported seeking medical care for their illness. Such surveys may be important tools for assessing the level of illness in the general population, including those who do not seek medical care and are thus not captured using traditional surveillance methods.