The two sexually transmitted infections most strongly associated with HIV acquisition in gay and bisexual men are anal warts and anal gonorrhoea, Australian researchers report in the online edition of the Journal of Acquired Immune Deficiency Syndromes.
Herpes infections did not emerge as significant in this study, but men with warts were three times more likely to acquire HIV, and men with gonorrhoea were seven times as likely. The authors suggest that more frequent screening for anal sexually transmitted infections in gay men should be investigated as a means of HIV prevention.
Numerous observational studies have suggested that sexually transmitted infections (STIs) facilitate the acquisition and transmission of HIV. However most studies have been conducted among heterosexuals, and previous prospective studies have not examined the full range of sexually transmitted infections that are common in gay and bisexual men.
In particular, genital or anal warts have often been overlooked, and many studies have not distinguished between genital and anal infections.
Warts are caused by infection with certain strains of the human papilloma virus (HPV). Infection with other strains of HPV may lead to cervical or anal cancer, but people with warts are not more likely to develop cancer. A recent study found that men infected with cancer-causing HPV are more likely to acquire HIV.
In the new study, 1,427 HIV negative homosexually active men in Sydney were recruited to the HIM (Health in Men) cohort and were interviewed about their risk behaviour twice a year. The average time men stayed in the study was just under four years.
Once a year, participants were offered a sexual health screen. This involved blood tests for HIV, syphilis and herpes simplex virus (HSV-1 and HSV-2). Gonorrhoea and chlamydia were both tested with urine and anal swab samples. In addition, at interviews, men were asked about recent diagnoses of STIs (including genital and anal warts, for which simple tests are not available).
A total of 53 men subsequently acquired HIV infection, and interview and STI data was available for 47 of them. The researchers analysed which STI diagnoses were associated with acquiring HIV during the same six month period.
In the first analysis, before controlling for differences in sexual behaviour, the following infections were all associated with HIV infection:
- Anal gonorrhoea
- Anal chlamydia
- Anal warts
- Genital warts
- HSV-1 (at baseline only)
Infections of gonorrhoea and chlamydia in the penis were not associated with acquiring HIV. Moreover, whereas HSV-1 infection at the beginning of the study was associated with acquiring HIV, subsequent HSV-1 infection or HSV-2 infection at either time were not. In most studies, it is HSV-2 that is most commonly associated with HIV infection, but the authors suggest that HSV-1 may be becoming more relevant in some industrialised countries.
The researchers then conducted an analysis which controlled for the number of times that men reported unprotected anal intercourse with a partner of unknown HIV-status or with an HIV-positive partner.
In this analysis, men who had anal gonorrhoea diagnosed by the researchers were seven times more likely to acquire HIV (hazard ratio 7.12; 95% confidence interval 2.05 - 24.75). Moreover, men who reported anal warts were over three times more likely to acquire HIV (hazard ratio 3.63; 95% confidence interval 1.62 - 8.14).
Association between other sexually transmitted infections and HIV acquisition was no longer statistically significant. However, it’s important to note that because the number of infections was relatively small in this sample, the study lacked statistical power to examine these relationships, and it is possible that a much larger study would identify an association.
The authors note that in most cases, the anal gonorrhoea diagnosed was asymptomatic. They suggest that it is plausible that long-standing infections, which can cause rectal inflammation, may be associated with HIV infection.
The researchers suggest two possible mechanisms by which warts may facilitate HIV transmission. Firstly, the warts themselves may weaken the integrity of the epithelial barrier to HIV. Secondly, the authors note that treatment for warts often produces ulceration and inflammation over a period of weeks or months, and it may be the treatment itself that increases the risk of infection.
The second suggestion would need to be validated by further research. Moreover, it may seem to be in contradiction with the authors’ conclusions and recommendations: “These findings suggest that frequent sexual health screening and prompt treatment of STIs, particularly anal STIs, should be investigated as potential means of HIV prevention in homosexual men.”
Jin F et al. Anal sexually transmitted infections and risk of HIV infection in homosexual men. . J Acquir Immune Defic Syndr, published online ahead of print, 2009. doi: 10.1097/QAI.0b013e3181b48f33