Epidemiological characteristics of the influenza pandemic (H1N1) 2009 in Germany based on the mandatory notification of cases

The aim of the investigation is the descriptive analysis of case-based information from mandatory notifications in the first year of the influenza pandemic (H1N1) 2009 in order to identify and describe epidemiological characteristics and risk factors for severe outcome. Four distinct time periods were defined to describe the age distribution of hospitalized and fatal cases. In contrast, stratified (age, sex) analysis of risk factors was carried out for the whole time period of pandemic influenza activity (notification weeks 18/2009 to 17/2010). Characteristic differences in the age distribution of reported cases were observed according to the time period. Among the reported risk factors, immunosuppression exhibited the highest probability for hospitalization or a fatal outcome (OR=8.82; CI95% 7.3-10.6 and OR=37.4; CI95% 25.5-54.8, respectively). The stratified analysis showed that this was especially pronounced for patients in the age group 60 years and above. Single case-based notifications of pandemic influenza have proven to be an invaluable source of information for assessing the epidemiological characteristics of the influenza pandemic 2009 in Germany. In addition, it allows comparative analysis of certain risk groups for severe disease. The information, thus, provides an important contribution for further developing and improving of public health recommendations.