Epidemiological study of health impact on influenza outpatients during 2008-2009 influenza season, Shonai, Yamagata

To make up for the lack of data on influenza-like illness (ILI), we studied patterns among 6,828 ILI patients seen at 34 healthcare facilities during the 2008-2009 influenza season in Shonai, Yamagata, Japan. Healthcare facilities were classified into 1) hospitals, 2) pediatric clinics, 3) internal medicine and pediatric clinics, 4) internal medicine clinics, and 5) others. The majority went to hospitals, but the highest percentage in all outpatient visits was 13.7% seen at pediatric clinics during the peak epidemiological week. Based on estimated incidence and hospitalization data for pandemic (H1N1) 2009 from Ministry of Health, Labour and Welfare, Japan, we estimated the number of ILI patients at 59,600-89,400 and the number hospitalized for pandemic (H1N1) 2009 at 895-2,240 in Shonai. If those with ILI follow the same consultation patterns as outpatients in the 2008/09 influenza season, this indicates an estimated 23,800-35,700 with ILI will go to hospitals and 20,040-30,060 to pediatric clinics during the H1N1 pandemic. This in turns means that an urgent need will arise for appropriate measures reducing this potentially huge burden during pandemic (H1N1) 2009 outbreak in Japan.