Infection with one subtype of the human papilloma virus (HPV) doubles the risk of becoming infected with HIV, and infection with several subtypes more than triples it, the third IAS conference heard on July 26th.
Dr. Peter Chin Hong from San Francisco told the conference that the EXPLORE trial of HIV-negative gay men in four US cities (Boston, Denver, New York and San Francisco) found that 81% of men who seroconverted (became HIV-positive) during a three-year period from January 2001 to January 2004 had HPV infection, as opposed to 50% of those who did not seroconvert.
Forty-three per cent of seroconverters had abnormal squamous cells in the anus, as opposed to 24% of non-seroconverters. The abnormal cells were extracted on swabs. Anal cytoscopy, which would have been able to detect the patches of anal intraepthelial neoplasia (AIN - abnormal and potentially precancerous skin) these cells came from, was not performed, which probably weakened the association between HIV infection and AIN, as swabs would not have detected every person with AIN.
The average number of HPV subtypes present in those infected was two. In univariate analysis, infection with one HPV subtype multiplied the risk of HIV infection by 2.0; with two subtypes by 2.4; and with three or more by 3.7.
However HPV infection was also associated with both unprotected anal sex and crystal meth use. Once these factors were adjusted for in multivariate analysis, the association of HPV seroconversion with infection with three or more subtypes of HPV remained statistically significant, multiplying the risk of HIV acquisition by 3.3. The presence of abnormal squamous cells multiplied the HIV risk by 2.8.
The study underlined the strong association between HIV acquisition and crystal meth use. Unprotected anal sex multiplied the likelihood of HIV acquisition by 7.2 but crystal meth use was almost as much a risk factor, multiplying the likelihood of acquisition by 6.8.
The EXPLORE trial followed up 1,409 HIV negative sexually active gay men between January 2001 and October 2002. There were 51 HIV infections in the group during the average three years of follow-up, an incidence of 1.2% a year. The median age of the group was 36; 78 per cent were white; the median number of sexual partners over the follow-up period was six; and 40% said they always used condoms during sex.
Dr. Chin Hong said that in studies of cervical cancer, there was an increased density of CD4 cells in patches of CIN (cervical intraepithelial neoplasia) compared with normal tissue, which suggests how the presence of HPV-associated skin lesions increases vulnerability to HIV infection.