[Surveillance of hepatitis A by molecular epidemiologic studies].

Hepatitis A virus was studied by molecular epidemiology in connection with an outbreak of hepatitis A associated with intravenous drug users (IVDU) in Norway. Hepatitis A virus was characterised by sequencing 114 of 1,242 notified cases of hepatitis A from January 1995 to July 1998. One hepatitis A variant (IVDU variant I) was detected among IVDU during an outbreak of hepatitis A, as well as among 19 out of 49 cases with no apparent association to this outbreak. During the autumn of 1997, a new variant (IVDU variant II) was detected in the IVDU communities. Genotyping of virus from imported cases associated with travel to endemic regions, revealed that they were distinct from the two other IVDU variants. Hepatitis A has disseminated among IVDU over years; this indicates that hepatitis A is endemic in these communities. At the turn of the year 1997/98, there was a smaller outbreak of hepatitis A among homosexual men in Oslo, distinguished by genotyping from the outbreaks in the IVDU communities. By molecular epidemiology we have been able to identify individual outbreaks of hepatitis A and distinguish them from the IVDU outbreak.