Heterosexually acquired HIV-1 infection: cases reported in England, Wales and Northern Ireland, 1985 to 1991.

By the end of 1991, there had been 417 reports of AIDS and 1620 reports of HIV-1 infection in persons in England, Wales and Northern Ireland who probably acquired their infection through sexual intercourse between men and women. Between 1986 and 1991, the proportion of AIDS cases attributable to heterosexual transmission increased from 2% to 14% and of diagnosed HIV-1 infections from 4% to 23%. Reported HIV-1 infections inadequately reflect the extent of infection as only individuals choosing to be tested can be reported. HIV-1 infection acquired during heterosexual intercourse may be the result of transmission from partners who were infected by routes other than heterosexual transmission (first generation transmission) or of transmission from infected partners who were themselves infected through heterosexual intercourse (second generation transmission). Of the 417 cases in which AIDS was acquired through heterosexual intercourse, 42 (10%) were categorised as due to first generation transmission, 328 (79%) as second generation transmission--abroad, and 47 (11%) as second generation transmission--UK. Transmission categories could be allocated to 1438 of the 1620 reports of HIV infection: 17% were categorised as first generation, 74% as second generation--abroad, and 9% as second generation--UK. Heterosexual transmission of HIV infection is increasing, both in individuals acquiring their infection abroad as well as those who become infected in the United Kingdom.