Many cases of chalmydia, when located in the rectum, have no symptoms. Because there are no symptoms, many people are infected and left untreated -- either because they have not presented for testing, or they present for testing but do not disclose that they engage in anal sex and therefore aren't tested for STIs in the rectum. This can be problematic.

A recent study was done to determine the rates of rectal chlamydia among gay men in the UK. They also looked at the proportion of infections that would have been missed without routine screening (ie. no symptoms, therefore no testing and treatment).

A total of 3076 men were screened. They found that 8.2% of the men had infection with Chlamydia (all serovars) in the rectum and 5.4% had infection in the urethra (pee tube). The majority of rectal infections (69.2%) were asymptomatic and would have been missed if routine screening had not been undertaken. 36 cases of LGV (lymphogranuloma venereum) were identitified.

The data show a high rate of rectal chlamydia infection, the majority of which were asymptomatic. As such, routine screening for rectal chlamydia in men at risk is important as this may represent an important 'reservoir' for the onward transmission of chlamydia (and LGV).

This is another reason why everyone should be screened routinely for STIs and not just after a possible exposure. You cannot wait for symptoms, to get a test.

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