Introduction: Hepatitis A virus (HAV) is one of the most important cause of fecally transmitted acute infectious hepatitis worldwide. In Hungary, beside the sporadic HAV infections, outbreaks also occur, particularly in Northeast part of the country where the subgenotype IA is endemic. The reported number of HAV cases was less than 10 per year in Southwest Hungary. Aims: A part of the European HAV surveillance, the author's aims were to follow and to analyze the outbreak of hepatitis A in Transdanubia (Southwest Hungary) in 2006 by molecular epidemiological methods. Materials and methods: Sera samples from symptomatic patients were tested prospectively by enzyme-immunoassay (EIA) and reverse transcription-polymerase chain reaction (RT-PCR) followed by sequence- and phylogenetic analysis. Results: Between June and December 2006, a total of 115 serum samples were positive for HAV IgM antibody in Southwest Hungary. Thirty (76.9%) of the 39 samples were RT-PCR-positive and contain genetically identical subgenotype IB hepatitis A virus (HAV/Transdanubia/2006/HUN) which has 100% nucleotide identity to strain IT-MAR-02 from Italy in 2002. Until now, approximately 1200-1300 persons have been infected with the probably imported strain. The average age of patients was 18 years (years 1 to 80). In this study, detailed clinical and epidemiological data of the outbreak are presented. Conclusions: Only the prospective molecular epidemiological study could verify the connection between the first sporadic HAV cases in June, the outbreak in August and the endemic spread of the virus since September in Southwest Hungary. This epidemic calls attention to how the hepatitis A outbreak can develop anywhere and at any time in Hungary and to the importance of active HAV immunization in the primer prevention.
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