Sexually transmitted infections increase HIV risk for gay men

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Certain sexually transmitted infections in the anus increase the risk of gay men becoming infected with HIV, according to research conducted in Sydney and presented to the Sixteenth International AIDS Conference in Toronto last week. In a separate study, the same team of investigators also found that gay men who were infected with herpes simplex virus-1 (HSV-1) were at a greater of risk of becoming infected with HIV.

There is epidemiological evidence suggesting a connection between sexually transmitted infections and the risk of HIV infection. It is therefore thought that preventing sexually transmitted infections could would also help to reduce the number of new HIV infections. Few studies have looked at the connection between sexually transmitted infections and the risk of becoming HIV-positive in gay men. Investigators from the Health in Men (HIM) study in Sydney, Australia, therefore conducted a prospective study involving over 1,400 HIV-negative gay men.

Comprehensive data were gathered on sexually transmitted infections and HIV risk behaviours. The investigators hypothesised that sexually transmitted infections would remain a risk factor for HIV even after unprotected insertive and receptive anal sex, the sexual activities associated with the greatest risk of HIV infection.


herpes simplex virus (HSV)

A viral infection which may cause sores around the mouth or genitals.


Receptive anal intercourse refers to the act of being penetrated during anal intercourse. The receptive partner is the ‘bottom’.

prospective study

A type of longitudinal study in which people join the study and information is then collected on them for several weeks, months or years. 


Insertive anal intercourse refers to the act of penetration during anal intercourse. The insertive partner is the ‘top’. 


A sexually transmitted infection caused by the bacterium Treponema pallidum. Transmission can occur by direct contact with a syphilis sore during vaginal, anal, or oral sex. Sores may be found around the penis, vagina, or anus, or in the rectum, on the lips, or in the mouth, but syphilis is often asymptomatic. It can spread from an infected mother to her unborn baby.

Every six months between 2001 and 2004, the men provided detailed information on their sexual behaviour. Specifically, they were asked to say on how many occasions, they had had unprotected receptive and insertive anal sex. They were also asked to say what the HIV status of the partners they had unprotected sex with was, and if ejaculation had occurred.

All the men in the study had an annual HIV test. They were also offered a comprehensive sexual health screen, including tests for gonorrhoea, syphilis, chlamydia, HSV-1 and HSV-2, hepatitis A virus, hepatitis B virus, and anal and genital warts. Individuals were also asked to report any incidences of gonorrohoea, syphilis, anogential warts or anogential herpes which they had experienced since their annual study sexual health screen.

The men had a median age of 35 years, and 42 become HIV-positive during the period of the study, yielding an incidence of 0.89 per 100 patient years.

Unprotected receptive anal sex with ejaculation a partner who was known to be HIV-positive (p

“These findings suggest that frequent sexual health screening and prompt treatment for sexually transmitted infections, may be an important means of HIV prevention in homosexual men”, conclude the investigators.

The investigators also gathered data on the baseline prevalence of, and incidence of new infections with, HSV-1 and HSV-2. Herpes simples virus (HSV) for short is a member of the herpes family. HSV is very common in the population and both types of HSV affect the ends of nerve cells in the skin. They can occasionally cause painful blisters to develop on the skin. HSV-1 is often called oral herpes and usually affects the lips and mouth; HSV-2 usually affects the anogential region.

Studies have shown that HSV-2 is significantly associated with an increased risk of HIV infection in heterosexuals, and the sexual transmission of HSV-1 is increasing in industrialised countries. However, there are few data on the importance of these infections to the risk of HIV acquisition in gay men.

At baseline, 75% of men were infected with HSV-1, 23% with HSV-2 and 19% with both. During the course of the study, 33 men became infected with HSV-1 and 28 with HSV-2.

There was evidence that HSV-1 was being sexually transmitted, as new infections with HSV-1 were associated with a greater number of sexual partners (p

In their analyses, the investigators found that being infected with HSV-1 (p = 0.025), but not HSV-2, at baseline was significantly associated with a risk of acquiring HIV. After adjusting for unprotected receptive anal sex with ejaculation with a man known to be HIV-positive, and unprotected anal sex receptive anal sex without ejaculation with a man of unknown HIV status, incident infection with neither HSV-1, nor HSV-2 was associated with an increased risk of HIV seroconversion.

“HSV-1 associated genital herpes may be a neglected co-factor predisposing to HIV infection”, write the investigators. Although data were not gathered on the site of HSV-1 ulcers, they believe that it is “plausible that anal infection…may be important.”


Grulich A et al. Anal sexually transmitted infections as risk factors for HIV infection in homosexual men: data from the HIM cohort. Sixteenth International AIDS Conference, Toronto, abstract TUAC0504, 2006.

Grulich A et al. Herpes simplex virus types 1 and 2 and HIV infection in homosexual men: data from the HIM cohort. Sixteenth International AIDS Conference, Toronto, abstract TUPE0280, 2006.