Clinical infectious diseases : an official publication of the Infectious Diseases Society of America
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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.
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A strong evidence base provides the foundation for planning and response strategies. Investments in pandemic preparedness included support for research that aided early detection, response, and control of the 2009 influenza A (H1N1) (pH1N1) pandemic. Scientific investigations conducted during the pandemic guided understanding of the virus, disease severity, and epidemiologic risk factors. ⋯ Communication of this evolving evidence base was important to sustaining credibility of public health. Areas where substantial controversy emerged, such as the optimal approach to respiratory protection of healthcare workers, often suffered from gaps in the evidence base. Many aspects of the 2009-2010 pandemic influenza experience provide ongoing opportunities for additional study, which will strengthen plans for future pandemic response as well as control of seasonal influenza.
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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. ⋯ 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.
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Given the potential worsening clinical severity of 2009 pandemic influenza A (H1N1) virus (pH1N1) infection from spring to fall 2009, we conducted a clinical case series among patients hospitalized with pH1N1 infection from September through October 2009. A case patient was defined as a hospitalized person who had test results positive for pH1N1 virus by real-time reverse-transcription polymerase chain reaction. Among 255 hospitalized patients, 34% were admitted to an intensive care unit and 8% died. ⋯ Chest radiographs obtained at hospital admission that had findings that were consistent with pneumonia were noted in 103 (46%) of 255 patients. Among 255 hospitalized patients, 208 (82%) received neuraminidase inhibitors, but only 47% had treatment started ≤ 2 days after illness onset. Overall, characteristics of hospitalized patients with pH1N1 infection in fall 2009 were similar to characteristics of patients hospitalized with pH1N1 infection in spring 2009, which suggests that clinical severity did not change substantially over this period.
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In April 2009, following the first school closure due to 2009 pandemic influenza A (H1N1) (pH1N1) in Chicago, Illinois, area hospitals were inundated with patients presenting with influenza-like illness (ILI). The extent of disease spread into the surrounding community was unclear. We performed a household survey to estimate the ILI attack rate among community residents and compared reported ILI with confirmed pH1N1 cases and ILI surveillance data (ie, hospital ILI visits, influenza testing, and school absenteeism). ⋯ Trends in surveillance data peaked during the same week and rapidly decreased to near baseline. Public awareness and health care practices impact standard ILI surveillance data. Community-based surveys are a valuable tool to help assess the burden of ILI in a community.