Gay men should have rectal tests for chlamydia as part of their routine sexual health care, investigators recommend in an article published in the online edition of Sexually Transmitted Infections. Researchers found that more gay men had rectal infection with chlamydia than had urethral chlamydia or rectal gonorrhoea. Furthermore, the majority of rectal chlamydia infections were asymptomatic and would therefore have been missed without routine testing.
They also found that over a third of the men with rectal chlamydia were HIV-positive.
Chlamydia is the most common bacterial sexually transmitted infection in the UK. Testing for urethral chlamydia is routinely offered to all men attending sexual health clinics. However, rectal testing for the infection is not offered to gay men attending most UK sexual health clinics. Nor is such screening recommended in the sexual health testing guidelines of the British Association for Sexual Health and HIV (BASHH).
Previous studies have found that between 7 and 9% of gay man attending sexual health clinics have rectal infection with chlamydia, and that such infections are often without symptoms. Chlamydia, like all sexually transmitted infections, can cause changes to the genital mucosa that increase the risk of HIV transmission. Therefore the investigators reasoned that a benefit of detecting and treating rectal chlamydia would be a reduction in onward HIV transmission.
In recent years, outbreaks of the sexually transmitted infection lymphogranuloma venereum (LGV) have been observed in gay men in the UK and several other industrialised countries. LGV is caused by certain strains of chlamydia. Most of the cases have involved rectal infection. In response to the outbreak of LGV, staff at London’s Chelsea and Westminster Hospital’s sexual health clinics started screening gay men for rectal chlamydia infection.
A study was designed by researchers from the hospital with three aims:
- To determine the prevalence of rectal chlamydia amongst gay men.
- To find out how many of these infections were asymptomatic.
- To establish the number of infections that would have remained undiagnosed had routine screening not been introduced.
The study was conducted between 2005 and 2006 and included a total of 3076 men. All these men had urethral screens for chlamydia and 3017 had rectal swabs for the infection.
Results showed that 8% of men had rectal chlamydia, with 5% having urethral chlamydia. The prevalence of chlamydia was higher than any other infection, with tests showing that 4% of men had rectal gonorrhoea, 5% had urethral gonorrhoea and 3% syphilis.
The investigators then looked at the cases of chlamydia in more detail. Of the 397 men diagnosed with chlamydia, 62% (247) were infected rectally, 42% (165) had urethral infection and 4% (15) had the infection in both sites.
Rectal infection with chlamydia was asymptomatic in 69% (171) of the men and would therefore have been missed without routine screening. Only 8% of asymptomatic men also had urethral infection.
Rectal LGV was diagnosed in 14% (35) of the men with rectal chlamydia. There was also one case of urethral LGV. The vast majority of rectal LGV cases (82%) were symptomatic.
There was a high prevalence of HIV infection in men with rectal chlamydia (38%, 94 individuals). The investigators also note that twelve men were first diagnosed with HIV at the same time as rectal infection with chlamydia was detected.
Factors significantly associated with rectal chlamydia were HIV infection (p < 0.01), rectal gonorrhoea (p = 0.0002) and genital warts (p = 0.016). The investigators excluded men with LGV from their statistical analysis, but they still found a significant association between rectal chlamydia and HIV (p = 0.004) and rectal chlamydia with rectal gonorrhoea (p = 0.002).
“Our data shows a higher rate of rectal chlamydia infection compared to gonorrhoea, a significant proportion of which were asymptomatic,” write the investigators.
They conclude, “current STI guidelines in the UK only recommend routine screening for rectal gonorrhoea but not rectal chlamydia and our data support the need to revisit these guidelines. We recommend routine screening for rectal chlamydia in men who have sex with men at risk of acquiring this infection.”
Annan NT et al. Rectal chlamydia – a reservoir of undiagnosed infection in MSM. Sex Transm Inf (online edition), 2009.