Gay men diagnosed with a rectal STI have a very high risk of subsequent infection with HIV

This article is more than 11 years old. Click here for more recent articles on this topic

The rate of new HIV infections is especially high among gay men recently diagnosed with a rectal sexually transmitted infection (STI), according to research conducted in New York City and published in the online edition of Clinical Infectious Diseases. 

The authors compared HIV incidence in both people diagnosed with rectal chlamydia (CT) and/or gonorrhoea (GC) infection at a baseline clinic visit between 2008 and 2010 and closely matched controls who were negative for these infections at their baseline visit. Over two-thirds of both the diagnosed people and the controls reported unprotected anal sex. During follow-up, 7% of men with rectal STIs at the initial clinic visit were diagnosed with HIV, compared to 3% of men without these infections at baseline. 

“Our results demonstrate that rectal CT/GC infections are objective markers for identifying persons at an exceptionally high risk for HIV,” comment the authors.



The last part of the large intestine just above the anus.


Chlamydia is a common sexually transmitted infection, caused by bacteria called Chlamydia trachomatis. Women can get chlamydia in the cervix, rectum, or throat. Men can get chlamydia in the urethra (inside the penis), rectum, or throat. Chlamydia is treated with antibiotics.

person years

In a study “100 person years of follow-up” could mean that information was collected on 100 people for one year, or on 50 people for two years each, or on ten people over ten years. In practice, each person’s duration of follow-up is likely to be different.


In a case-control study, a process to make the cases and the controls comparable with respect to extraneous factors. For example, each case is matched individually with a control subject on variables such as age, sex and HIV status. 

CAT scan

A computerised axial tomography (CAT) or computed tomography (CT) scan is a type of specialised X-ray that gives a view of a 'slice' through the body, and is used to help detect tumours, infections and other changes in anatomy.

Gay and other men who have sex with men (MSM) are one of the groups most affected by HIV. Almost half of new HIV infections in New York City in 2010 involved gay men, and very high rates of STIs have also been recorded in this population. STIs can cause biological changes that increase susceptibility to infection with HIV.

Unprotected anal intercourse is a well-known risk factor for HIV infection for gay men. The presence of a rectal STI can be considered a marker of high-risk sexual behaviour. Investigators wished to see if recent diagnosis with a rectal chlamydia and/or gonorrhoea was associated with an increased risk of subsequent HIV infection.

Their study population consisted of 276 gay men who were screened for HIV and STIs at the same clinic visit between 2008 and 2010. The men tested HIV negative but all were diagnosed with a rectal STI (chlamydia, n= 177; gonorrhoea, n = 69; both, n = 30). Over two-thirds (69%) reported no or inconsistent condom use and a median of four partners in the previous three months. Most of the rectal infections (70%) were asymptomatic, “underscoring the need for routine rectal screening of patients who report unprotected anal intercourse”.

The participants were matched with 276 controls, gay men who tested negative for both HIV and rectal STIs at a clinic visit in the same period. These controls had a similar HIV risk profile to the diagnosed participants, with 69% also reporting no or inconsistent condom use.

Both the diagnosed participants and controls were followed for at least one year.

During a total of 464 person-years of follow-up, 11% of men with a rectal STI at baseline were diagnosed with HIV, an annual HIV incidence rate of 11%. HIV incidence was especially high among some groups with rectal STIs. These included black men (15%); men with both chlamydia and gonorrhoea (10%); and those aged under 20 (10%).

The control group participants contributed 474 person-years of follow-up. A total of twelve individuals (4%) were diagnosed with HIV, an annual incidence rate of (3%).

The investigators therefore calculated that men with rectal STIs were significantly more likely to be diagnosed with HIV during follow-up (relative risk, 2.58; 95% CI, 1.33-5.03).

“Identifying and treating rectal infections may reduce HIV incidence, to the extent rectal STDs increase biological susceptibility to HIV infection through epithelial erosions and alteration in host immune defences,” the authors conclude. “Rectal infections, as markers of behavioural risk, can be used to identify a subset of patients who may benefit from intensive risk reduction counselling and other interventions designed to reduce the risk of HIV transmission.”


Pathela P et al. HIV incidence among men with and those without sexually transmitted rectal infections: estimates from matching against an HIV case registry. Clin Infect Dis, online edition, 2013.