Background: PrEP is highly effective, although PrEP persistence has been limited in real world PrEP implementation. Little is known about the HIV risk after stopping PrEP and the experience of individuals who stop PrEP and later HIV seroconvert.
Methods: We identified individuals who initiated PrEP in the San Francisco Primary Care Clinics (SFPCC), a 15-clinic safety-net integrated delivery system, and performed in-depth chart review to determine person-time on and after stopping PrEP through 11/2018. We identified all PrEP seroconversions using the CDC''s Enhanced HIV/AIDS Reporting System. We calculated the HIV incidence using Poisson models while individuals were using PrEP and after stopping. We performed in-depth interviews with patients who seroconverted.
Results: Overall, 986 individuals initiated PrEP, with a median age of 35; 12% were transwomen, 66% MSM 12% Black, and 26% Latino. There were 895 person-years (P-Y) of follow-up on PrEP and 953 after stopping PrEP. The HIV incidence on PrEP was eight-fold higher after stopping PrEP compared to while on PrEP (95% CI 1-336; p=0.03; 0.8 vs. 0.1/100 person-years). Of the eight individuals who HIV seroconverted, three were transwomen, five MSM; only one was taking PrEP at the time of seroconversion. Of the seven individuals who seroconverted after stopping PrEP, two stopped due to side effects, one after changing insurance, one moved and lost access to PrEP care, one moved into a shelter and lost his pills, one relapsed on methamphetamine, and one stopped due to entering a stable relationship. All but one received primary care services after stopping PrEP; most reported difficulty assessing their HIV risk and anger that they had not received additional outreach while on PrEP. The individual who developed HIV while taking PrEP reported taking intermittent PrEP during all sexual encounters, although was incorrectly taking one rather than two pills prior to sex.
Conclusions: The HIV incidence after stopping PrEP was eight-fold higher than while on PrEP. Many individuals who stop PrEP remain at risk of HIV, and proactive outreach could potentially have prevented many of the HIV infections in this cohort. Individuals using non-daily PrEP should be provided additional education and support.

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