Can we screen less frequently for STI among PrEP users? Assessing the effect of biannual STI screening on timing of diagnosis and transmission risk in the AMPrEP Study

Abstract

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.

Bacterial sexually transmitted infections are concentrated in subpopulations of MSM using HIV PrEP: an analysis of longitudinal trajectories

“…Modelling studies have shown that more frequent screening could reduce the incidence of chlamydia, gonorrhea and syphilis [20][21][22], but these results have not been corroborated by empirical studies on opportunistic testing [23,24] these STIs and possible onward transmission [13,14]. However, screening for STIs, primarily chlamydia and gonorrhea, is costly and screening 6-monthly is more cost-effective than 3-monthly [25].…”

“…While 3-monthly STI screening leads to earlier diagnosis and treatment of, primarily, asymptomatic bacterial STIs compared to 6-monthly screening [ 13 , 14 ], not all PrEP users may need testing at this frequency. Previous studies from Australia found that half of their participants were not diagnosed with any STI within one year of follow-up and that the majority of STIs were concentrated within a small subpopulation [ 7 , 9 ].…”

“…In addition, certain socio-demographic and behavioral characteristics (e.g. younger age, use of chemsex and condomless anal sex) have been associated with an increased risk of bacterial STIs [ 7 , 14 ]. Further characterization of subpopulations of PrEP users at increased risk for STIs may offer an opportunity for more targeted bacterial STI screening, which could reduce monitoring burden for PrEP users and costs.…”

Determining the screening frequency for sexually transmitted infections for people who use HIV pre-exposure prophylaxis: a systematic review and meta-analysis

“…Although using 3-monthly rather than 6-monthly STI screening could detect more infections [30] , an important consideration for recommending frequent STI screening is the increased need for antibiotics. An analysis of national and sentinel surveillance data in England (2015-2019) indicated that there was increasing gonococcal AMR, especially among MSM populations compared to heterosexual couples [31] .…”

Sexually transmitted infection testing and prevalence among MSM using event-based dosing HIV pre-exposure prophylaxis

“…Modelling data in Europe suggests that reducing STI testing frequency in asymptomatic MSM using PrEP, can result in significant delays in STI diagnosis including syphilis. 12 The increased testing for STIs in MSM driven by PrEP use is associated with increased macrolide use and risk of increasing rates of antimicrobial resistance. 13 A delayed diagnoses of syphilis due to a reduction in STI screening in MSM using PrEP could result in serious sequelae.…”