An HIV type 1 subtype A outbreak among injecting drug users in Latvia.

Local, explosive outbreaks of HIV-1 infections among intravenous drug users (IDUs) caused by closely related variants have been reported in the Ukraine and Russia since 1996. Latvia experienced the start of a similar outbreak at the end of 1997 and already at the end of 1998 IDUs constituted approximately 50% of all known HIV cases (122 of 251). To investigate the molecular epidemiology of HIV-1 variants circulating among Latvian IDUs the V3 domain of the env gene was directly sequenced from samples of seven recently infected IDUs. Phylogenetic tree analysis showed that the seven Latvian HIV-1 variants had closely related subtype A genotypes that shared recent ancestry with each other as well as with variants involved in outbreaks in the Ukraine and southern Russia. There exists a clear risk for continued spread of HIV-1 in Latvia because the number of IDUs is increasing and needle sharing is common.