The proportion of heterosexuals in the UK infected with HIV subtype B has fallen significantly in recent years, according to data presented to the annual scientific conference of the UK’s Public Health Laboratory Service (PHLS).
Gary Murphy of the Sexually Transmitted and Bloodborne Virus Laboratory told delegates that using a combination of ultra sensitive and sensitive HIV tests 802 recent HIV infections amongst heterosexuals were detected between 1997 and 1999. Using both tests it is possible to accurately detect recent subtype-B infections within 170 days of infection. However the technique is less able to accurately pin-point recent subtype A and C infections, with a window period of almost a year.
Between 1997 and 1999, the proportion of subtype B new HIV infections amongst heterosexuals fell to less than 5% in 1999. During the same period, the number of heterosexuals found to be recently infected with non-B subtypes increased, in particular HIV subtypes A, C and subtype AG.
As non-B subtype infections could have happened within the past year, Dr Murphy said it was not possible to say if the infections had happened in the UK, but that he suspected that the overwhelming number of heterosexual infections were acquired outside the UK, particularly in sub-Saharan Africa.
In response to a question from the floor, Dr Barry Evans of the PHLS said that there was no evidence that people with non-subtype B experienced faster disease progression in the UK. However, some recent studies have suggested that both protease inhibitors and NNRTIs may be less effective against subtype C.
Dr Murphy admitted limitations to his study, not least the very small number of new heterosexual cases of HIV detected each year (approximately 150) in this study.
Whilst the number of new subtype B infections fell overall amongst heterosexuals regardless of sex, they remained disproportionately concentrated amongst men. Some researchers have speculated that heterosexual men are more likely to be infected with subtype B HIV, which is the form of HIV most common amongst gay men in Europe and the USA, due to covert homosexual behaviour which has not been admitted at the time of HIV testing.
Murphy G et al. Identification of incident HIV infections among heterosexuals attending STI clinics. PHLS Annual Conference, oral presentation, 10 September, 2002.