Prevalence and correlates of and a risk score to identify asymptomatic anorectal gonorrhoea and chlamydia infection among men who have sex with men in Kisumu, Kenya.

Objectives: In settings where laboratory capacity is limited, the WHO recommends presumptive treatment for (NG) and (CT) in asymptomatic men who have sex with men (MSM) at high risk for these infections. However, little is known about how best to target this intervention. We aimed to identify correlates of anorectal NG/CT infection in Kenyan MSM with and without anorectal symptoms and evaluate the performance of an empirical, model-based risk score to identify cases in asymptomatic men.

Methods: Anorectal NG/CT infections were diagnosed by the Abbott RealTime NG/CT nucleic acid amplification testamong 698 MSM at enrolment into the Anza Mapema study. Multivariable logistic regression was used to identify correlates of anorectal NG/CT infection in men with and without anorectal symptoms. Using coefficients from the final multivariable model for asymptomatic men, we calculated a risk score for each participant. Risk score performance was determined by calculating the sensitivity, specificity and number needed to treat (NNT) to identify one NG/CT infection.

Results: Overall anorectal NG/CT infection prevalence was 5.2% (n=36), of which 58.3% (n=21) were asymptomatic. Factors associated with anorectal NG/CT infection in asymptomatic men were aged 18-24 years (aOR=7.6; 95% CI: 1.7 to 33.2), HIV positive serostatus (aOR=6.9; 95% CI: 2.2 to 21.6) and unprotected anal sex in the past 3 months (aOR=3.8; 95% CI: 1.2 to 11.9). Sensitivity and specificity were optimal (81.0% and 66.1%, respectively) at a model-derived risk score cut-point ≥3, and the NNT was 12.

Conclusions: A model-derived risk score based on correlates of anorectal NG/CT infection in asymptomatic participants would be sensitive and efficient (i.e, low NNT) for targeting presumptive treatment. If validated in other settings, this risk score could improve on the WHO algorithm and help reduce the burden of asymptomatic anorectal NG/CT infections among MSM in settings where diagnostic testing is not available.