Dynamics of the HIV-1 subtype distribution in the Swedish HIV-1 epidemic during the period 1980 to 1993.

We have investigated the distribution of the major subtypes, or clades (A to E), in the Swedish human immunodeficiency virus type 1 (HIV-1) epidemic between the years 1980 to 1993, using gp120 V3 domain serotyping and genotyping. Until 1984 the Swedish HIV-1 epidemic was almost exclusively caused by HIV-1 subtype B. During the late 1980s and the early 1990s an increase in nonsubtype B infections (mainly subtypes A and C) was observed. Nonsubtype B infections constituted approximately 30% of the newly diagnosed HIV-1 cases in 1993. In the analyzed material we also noted a substantial increase in the proportion of HIV-1 infections caused by heterosexual transmission. The present data suggest that the subtype distribution in the Swedish HIV-1 epidemic may well continue to change with time, which may have implications for preventive research and vaccine development strategies.