The most recent transmission chain identified by the study shows a faster doubling time in 2003 than the other five. Current surveillance data shows a recent increase in infections amongst homosexual men in the UK , which may partly have come through this chain.
Dr Deenan Pillay of UCL's Centre for Virology says: “Our study suggests that the HIV-1 subtype B epidemic currently circulating the UK is made up of at least six established chains of transmission, introduced in the early and mid 1980s. This goes against the prevailing belief that one initial entry of HIV-1 was responsible for the spread of the epidemic.
“Since 1990 there have been important changes in Britain's social attitudes and awareness of HIV-1 and AIDS. Despite a very recent increase in high-risk behaviour among men having sex with men, a significant increase in condom use has been reported since 1990, which could explain the equilibrium reached for the number of infections.
“Antiretroviral therapy may also have impacted on transmission rates, but our evidence does not demonstrate this. You would expect growth rates to decrease in the late rather than early 1990s around the time that potent therapy became widely used if this was the case. Instead, we see little correlation between widespread availability of treatment and reduction of transmission. This is highly pertinent to the recent increase again in new HIV-1 diagnoses within the UK .
“Our study also contradicts assumptions that the HIV-1 epidemic is composed of smaller, independent epidemics defined by risk group, where we have found evidence for at least six larger sub-epidemics, which HIV monitoring, prevention and treatment programmes may want to take into account when developing new initiatives.?/p>
More than 57,700 people in Britain have been infected with human immunodeficiency virus type 1 or HIV-1 since the first identification of A ID