Objective

Evaluate the incidence and predictors of HIV acquisition from outside partners in serodiscordant couples.

Methods

Demographic, behavioral, and clinical exposures were measured quarterly in a cohort of serodiscordant cohabiting couples in Zambia from 1995 to 2012 (n = 3049). Genetic analysis classified incident infections as those acquired from the study partner (linked) or acquired from an outside partner (unlinked). Factors associated with time to unlinked HIV infection were evaluated using multivariable Cox proportional hazards regression stratified by sex.

Results

There were 100 unlinked infections in couples followed for a median of 806 days. Forty-five infections occurred in women [1.85/100 couple-years; 95% confidence interval (CI): 1.35 to 2.47]. Risk of female unlinked infection (vs. nonseroconverting females) was associated with reporting being drunk weekly/daily vs. moderate/nondrinkers at baseline [adjusted hazard ratio (aHR) = 5.44; 95% CI: 1.03 to 28.73], genital ulcers (aHR = 6.09; 95% CI: 2.72 to 13.64), or genital inflammation (aHR = 11.92; 95% CI: 5.60 to 25.37) during follow-up adjusting for age, years cohabiting, income, contraceptive use, previous pregnancies, history of sexually transmitted infections, and condomless sex with study partner. Fifty-five infections occurred in men (1.82/100 couple-years; 95% CI: 1.37 to 2.37). Risk of male unlinked infection was associated with genital inflammation (aHR = 8.52; 95% CI: 3.82 to 19.03) or genital ulceration (aHR = 2.31; 95% CI: 2.05 to 8.89), reporting ≥1 outside sexual partner (aHR = 3.86; 95% CI: 0.98 to 15.17) during follow-up, and reporting being drunk weekly/daily vs. moderate/nondrinkers at baseline (aHR = 3.84; 95% CI: 1.28 to 11.55), controlling for age, income, circumcision status, and history of sexually transmitted infection.

Conclusions

Predictors of unlinked infection in serodiscordant relationships were alcohol use, genital inflammation, and ulceration. Causes of genital inflammation and ulceration should be screened for and treated in HIV-negative individuals. Counseling on risk of alcohol use and sex with outside partners should be discussed with couples where 1 or both are HIV-negative, including in counseling on use of pre-exposure prophylaxis to prevent HIV acquisition in the HIV-negative partner (when feasible and affordable).