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ObjectivesAdherence is key to the effectiveness of oral pre-exposure prophylaxis (PrEP) to prevent HIV. Therefore, we aimed to explore factors associated with adherence to daily PrEP (dPrEP).MethodsMen who have sex with men (MSM) using dPrEP (emtricitabine/tenofovir disoproxil) within the Amsterdam PrEP demonstration project at the Public Health Service of Amsterdam, provided dried blood spots (DBS) 12 and 24 months after PrEP initiation. From DBS, we determined intracellular tenofovir diphosphate (TFV-DP) concentrations to assess adherence; TFV-DP ≥700 fmol/punch was considered adequate. We assessed associations of sociodemographic, clinical and behavioural characteristics with TFV-DP concentrations using multivariable linear regression.ResultsOf 263 participants who attended 12-month or 24-month study visits while on dPrEP, 257 (97.7%) provided DBS at one or both visits (492 DBS in total). Median TFV-DP concentration was 1299 (IQR 1021–1627) fmol/punch (12 months: 1332 (1087–1687); 24 months: 1248 (929–1590]). Higher TFV-DP concentrations were associated with: older age (p=0.0008), condomless anal sex with a casual partner in 6 months preceding PrEP initiation (+166 fmol/punch; 95% CI 36.5 to 296) and using a mobile application providing visualised feedback on PrEP use and sexual behaviour (+146 fmol/punch; 95% CI 28.1 to 263). Lower TFV-DP concentrations were associated with longer duration of PrEP use (24 vs 12 months; −91.5 fmol/punch; 95% CI −155 to −28.1). Time-updated number of sex partners, diagnosed STIs and chemsex were not associated with TFV-DP concentrations.ConclusionsOverall, TFV-DP concentrations were high among MSM using dPrEP, indicating excellent adherence. Especially older participants, those who reported condomless anal sex with a casual partner prior to PrEP initiation and those who used an app with visualised feedback showed higher levels of adherence. As TFV-DP concentrations had decreased slightly at 2 years of PrEP use when compared with 1 year, we emphasise the importance of adherence counselling to those who continue using PrEP.Trial registration numberNL5413.

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.

Pre-exposure prophylaxis (PrEP) for HIV might induce risk compensation, defined as increased sexual risk behaviour leading to increased incidence of bacterial sexually transmitted infections (STIs). We examined the incidence of HIV, STIs, and sexual behaviour after initiating daily and event-driven PrEP.

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