Objective: To determine the prevalence of rectal chlamydia infection in a cohort of men who have sex with men (MSM) and the proportion of infection that would be missed without routine screening.
Methods: MSM presenting to four HIV/GUM outpatient clinics at the Chelsea & Westminster Hospital NHS Foundation Trust between 1 November 2005 and 29 September 2006 were offered testing for rectal chlamydia infection in addition to their routine screen for sexually transmitted infections (STIs). Chlamydia trachomatis (CT) tests were performed using the Beckton-Dickinson Probe-Tec Strand Displacement Assay. Positive samples were re-tested at the Sexually Transmitted Bacteria Reference Laboratory, to confirm the result and identify lymphogranuloma venereum (LGV)-associated serovars.
Results: A total of 3076 men were screened. We found an 8.2% prevalence of infection with CT (LGV and non-LGV serovars) in the rectum and 5.4% in the urethra. The HIV and rectal chlamydia co-infection rate was 38.1%. The majority of rectal infections (69.2%, (171/247)) were asymptomatic and would have been missed if routine screening had not been undertaken. Of the samples re-tested, 94.2% (227/242) rectal and 91.8% (79/86) urethral specimens were confirmed CT positive and 36 cases of LGV were identified.
Conclusion: Our data show a high rate of rectal chlamydia infection, in the majority of cases it was asymptomatic. We recommend routine screening for rectal chlamydia in men at risk, as this may represent an important reservoir for the onward transmission of infection.
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See Editorial, p 157
Competing interests: None.
Contributors: NTA, AN, PN, AM and MR were involved in collecting and analysing the data. SA was involved in testing all the chlamydia positive specimens and genotyping for LGV serovars at the STBRL. BA is the lead microbiologist at our centre responsible for coordinating the testing of laboratory specimens and liaising with the STBRL. HW was responsible for initiating the case finding exercise in collaboration with the STBRL. SM specialised in the statistical analysis and NTA, AN, AS, HW and NN wrote the final manuscript.