Laboratory-based assessment of influenza in German ambulant patients from 1998 to 2008

Abstract

In Germany, the cost for PCR diagnosis of influenza in ambulant patients was not covered by the national statutory health insurance system until 2008. Therefore, cell culture was the standard method applied for routine diagnosis. We have prospectively compared a 1-day rapid cell culture assay (RCA) with conventional cell culture (CCC) during the influenza seasons from 1997/1998 to 2007/2008 and with real-time PCR analysis during the influenza seasons 2003/2004 and 2006/2007. This study is based on 4,262 respiratory samples obtained from ambulant patients between January 1998 and May 2008. The RCA was performed in microtiter plates that were stained with monoclonal antibodies to influenza virus A and B 16 h after inoculation. A total of 1,221 specimens were found to be positive by the cell culture methods - 1,143 (93.6%) by the RCA and 1,012 (82.9%) by the CCC. The sensitivity of the RCA and CCC versus PCR was 75.4% (221/293) and 58% (170/293), respectively. The specificity of both cell culture assays versus PCR was 100%. Influenza A represented 79.3% of the cases diagnosed. An increased activity of influenza was observed between January and March, with the rate of influenza-positive cases being highest for kindergarten and school-aged children. While PCR is the most sensitive assay for the diagnosis of influenza, the RCA can still be used for diagnosis and surveillance of this disease. Based on our findings and given the known fact that influenza antibodies reach a plateau 2-4 weeks after immunization, the optimal time for vaccination in Germany is from October through November. Kindergarten and school-aged children represent an important reservoir of infection. Consequently, routine immunization should be considered for this age group to prevent the spread of influenza.