Incidence of HIV Infection in People Under Post-exposure Prophylaxis: A Cohort Study

Abstract

Background: Post-exposure prophylaxis (PEP) is a critical intervention for preventing HIV infection after high-risk occupational and non-occupational exposures. Timely referral for, and initiation of, PEP are essential to reduce the risk of transmission. Objectives: This study aimed to compare HIV incidence and programmatic outcomes between individuals presenting within 72 hours of exposure, who received PEP according to national guidelines, and those presenting after 72 hours, who generally did not receive PEP, reflecting real-world clinical practice. Methods: In this prospective cohort study, 149 participants referred to the Behavioral Diseases Counseling Center at Imam Khomeini Hospital in Tehran from April to July 2019 were enrolled and followed for up to six months. Participants were divided into two groups according to referral time: ≤ 72 hours (n = 74) and > 72 hours (n = 75). Participants in the early-referral group received a standard PEP regimen, and adherence was assessed by self-report. All participants were followed monthly for six months after exposure, and HIV testing was performed at three and six months using enzyme-linked immunosorbent assay (ELISA). The primary outcome was HIV seroconversion at six months post-exposure. Secondary outcomes included adherence to the PEP regimen, completion of therapy, and occurrence of re-exposure. Results: In the early-referral group, adherence to the PEP regimen was 95.9%. No participants in either group seroconverted at six months. Demographic characteristics differed slightly between the groups; most participants were male, single, and had a university education. The mean time from exposure to referral was 35.11 hours in the early group and 26.47 days in the late group. Few cases of sexual re-exposure were observed, and no occupational re-exposure occurred. Conclusions: Although no HIV seroconversions were observed, timely initiation of PEP remains strongly recommended in accordance with World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) guidelines to reduce cumulative HIV transmission risk. Early referral, adherence to prophylaxis, and standardized counseling remain key components of post-exposure management. This study did not evaluate the effectiveness of PEP beyond 72 hours but reflects real-world timing of presentation and its implications for post-exposure management.