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WMJ. 2010 Aug;109(4):201-8.

Epidemiologic and clinical features among patients hospitalized in Wisconsin with 2009 H1N1 influenza A virus infections, April to August 2009.

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  • 1Bureau of Communicable Diseases and Emergency Response, Wisconsin Division of Public Health, Madison, WI 53701-2659, USA.



During April 15 through July 23, 2009, Wisconsin reported the most confirmed and probable cases of 2009 influenza A (H1N1) virus (2009 H1N1) infection in the United States. Preliminary reports suggest that 2009 H1N1 infection disproportionately affected minority populations.


Prospective surveillance among all acute care hospitals in Wisconsin to detect patients hospitalized at least 24 hours with confirmed 2009 H1N1 infection during April 23 through August 15, 2009.


During the study interval, 252 patients were hospitalized and 11 (4%) died. Statewide hospitalization rates by age, sex, and race/ethnicity categories were highest among patients aged <1 year (21.6/100,000), females (4.9/100,000), and African Americans (36.3/100,000). The median age was 28 years: Hispanics (median age=16 years) and African Americans (24 years) were younger than non-Hispanic whites (37 years) and Asians (38 years). African Americans were more likely to have a hematologic condition and be morbidly obese (BMI > or = 40 kg/m2), and less likely to be admitted to an intensive care unit compared to other race/ethnicity groups (P<0.05). Hispanics and non-Hispanic whites were more likely to have cancer, be non-morbidly obese (BMI 30-39.9 kg/m2 or BMI percentile > or = 95%), and be hospitalized for >5 days compared to African Americans and Asians (P<0.05). There were no significant racial/ethnic differences in time from illness onset to admission or receipt of antiviral therapy, need for mechanical ventilation, acute respiratory distress syndrome, or death.


The first wave of the 2009 H1N1 pandemic in Wisconsin disproportionately affected hospitalized patients who were African Americans, Asians, and Hispanics compared to non-Hispanic whites. Preventive measures focused on these populations may reduce morbidity associated with 2009 H1N1 infection.

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