BackgroundIn many countries, HIV pre-exposure prophylaxis (PrEP) users are screened quarterly for STIs. We assessed the consequences of less frequent STI testing. We also assessed determinants of asymptomatic STI and potential for onward transmission.MethodsUsing data from the AMPrEP study, we assessed the proportion of syphilis, and genital, anal, and pharyngeal chlamydia and gonorrhoea diagnoses which would have been delayed with biannual versus quarterly screening. We assessed the potential for onward transmission by examining reported condomless anal sex (CAS) in periods after to-be-omitted visits when screening biannually. We assessed determinants of incident asymptomatic STIs using Poisson regression and calculated individual risk scores on the basis of the coefficients from this model.ResultsWe included 366 participants. Median follow-up was 47 months (IQR 43–50). 1,183STIs were diagnosed, of which 932(79%) asymptomatic. With biannual screening, 483 asymptomatic STIs (52%) diagnoses would have been delayed at 364 study visits. Of these visits, 129 (35%), 240 (66%) and 265 (73%) were followed by periods of CAS with steady, known casual or unknown casual partners, respectively. Older participants had a lower risk of asymptomatic STI (incidence rate ratio (IRR) 0.86/10-year increase, 95% CI 0.80 to 0.92), while CAS with known (IRR 1.36, 95% CI 1.10 to 1.68) and unknown (IRR 1.86, 95% CI 1.48 to 2.34) casual partners and chemsex (IRR 1.51, 95% CI 1.28 to 1.78) increased the risk. The individual risk scores had limited predictive value (sensitivity=0.70 (95% CI 0.66 to 0.74), specificity=0.50 (95% CI 0.48 to 0.51)).ConclusionReducing the STI screening frequency to biannually among PrEP users will likely result in delayed diagnoses, potentially driving onward transmission. Although determinants for asymptomatic STIs were identified, predictive power was low.

BackgroundAnorectal infections with Chlamydia trachomatis (CT) are common in women visiting STI outpatient clinics. We here evaluated the risk posed by sexual exposure and by alternate anatomical site infection for incident anorectal and urogenital CT.MethodsProspective multicentre cohort study, FemCure. Participants were treated for CT, and after 4, 6, 8, 10 and 12 weeks, they self-collected anorectal and urogenital samples (swabs) for CT-DNA testing. We calculated the proportion with incident CT, that is, CT incidence (at weeks 6–12) by 2-week time-periods. Compared with no exposure (A), we estimated the risk of incident CT for (B) sexual exposure, (C) alternate site anatomic site infection and (D) both, adjusted for confounders and expressed as adjusted ORs with 95% CIs.ResultsWe analysed data of 385 participants contributing 1540 2-week periods. The anorectal CT incidence was 2.9% (39/1343) (95 CI 1.8 to 3.6); 1.3% (A), 1.3% (B), 27.8% (C) and 36.7% (D). The ORs were: 0.91 (95% CI 0.32 to 2.60) (B), 26.0 (95% CI 7.16 to 94.34) (C), 44.26 (95% CI 14.38 to 136.21) (D).The urogenital CT incidence was 3.3% (47/1428) (95% CI 2.4 to 4.4); 0.7% (A), 1.9% (B), 13.9% (C) and 25.4% (D). The ORs were: 2.73 (95% CI 0.87 to 8.61) (B), 21.77 (95% CI 6.70 to 70 71) (C) and 49.66 (95% CI 15.37 to 160.41) (D).ConclusionsAfter initial treatment, an alternate anatomical site CT infection increased the risk for an incident CT in women, especially when also sex was reported. This may suggest a key role for autoinoculation in the re-establishment or persistence of urogenital and anorectal chlamydia infections.