IAS: HPV infection is an independent risk factor for HIV

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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.

Glossary

human papilloma virus (HPV)

Some strains of this virus cause warts, including genital and anal warts. Other strains are responsible for cervical cancer, anal cancer and some cancers of the penis, vagina, vulva, urethra, tongue and tonsils.

subtype

In HIV, different strains which can be grouped according to their genes. HIV-1 is classified into three ‘groups,’ M, N, and O. Most HIV-1 is in group M which is further divided into subtypes, A, B, C and D etc. Subtype B is most common in Europe and North America, whilst A, C and D are most important worldwide.

anal intraepithelial neoplasia (AIN)

An abnormal growth on the surface of the rectum or anal canal which, when observed with a microscope, suggests that the cells could be malignant (cancerous).

cervix

The cervix is the neck of the womb, at the top of the vagina. This tight ‘collar’ of tissue closes off the womb except during childbirth. Cancerous changes are most likely in the transformation zone where the vaginal epithelium (lining) and the lining of the womb meet.

cervical intraepithelial neoplasia (CIN)

Changes to cervical tissue which can be seen on visual examination through a colposcope. These are graded CIN1 to 3 according to severity. CIN1 is often left untreated; higher-grade lesions will probably need removing.

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.