Background
Highly efficacious oral pre-exposure prophylaxis (PrEP) is the global standard for HIV-1 prevention, including in clinical trials of novel PrEP agents using active-comparator designs. The analysis assessed whether incident sexually transmitted infections (STI) can serve as a surrogate indicator of HIV-1 incidence that might occur in the absence of PrEP.
Methods
We analyzed data from 3256 women randomized to placebo groups of oral and vaginal PrEP trials (MTN-003/VOICE and MTN-020/ASPIRE). Regression modelling assessed the correlation between incident individual STIs (Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis, each considered separately) and incident HIV-1.
Results
Across 18 sites in 4 countries (Malawi, South Africa, Uganda, Zimbabwe) STI and HIV-1 incidences were high: HIV-1 4.9, N. gonorrhoeae 5.3, C. trachomatis 14.5, and T. vaginalis 7.1 per 100 person-years. There was limited correlation between HIV-1 incidence and incidence of individual STIs: N. gonorrhoeae (r=0.02, p=0.871), C. trachomatis (r=0.49, p=<0.001), and T. vaginalis (r=0.10, p=0.481). The modest association with C. trachomatis was driven by country-level differences in both C. trachomatis and HIV-1, with no statistically significant association within countries.
Conclusions
STI incidence did not reliably predict HIV-1 incidence at the population level amongst at-risk African women participating in two large PrEP trials.