Enrollment and retention of HIV discordant couples in Lusaka, Zambia

Background: Biased enrollment and attrition compromise the power of clinical trials and limit generalizability of findings. We identify predictors of enrollment and retention for HIV-discordant couples enrolled in prospective studies in Zambia. Principal Findings: A total of 1995 discordant couples were invited to enroll. Predictors of nonenrollment, loss to follow-up, and missed appointments were evaluated using multivariate models. M+F- couples were more likely to be eligible and to enroll and less likely to be lost to follow-up than F+M- couples. Substantial losses to follow-up occurred between testing and enrollment (21.3% of M+F- and 28.1% of F+M-) and between enrollment and the first follow-up visit (24.9% of M+F- and 30.5% of F+M-). Among M+F- and F+M- couples, residence far from the clinic, younger age, and women's age at first intercourse 17 years were predictive of attrition. No income, <= 2 lifetime sex partners, no history of sexually transmitted infection in women, and recent extramarital contact in their male partners predicted attrition in F+M- couples. Conclusions: Discordant couples are critical to observational studies and clinical trials to prevent male-to-female and female-to-male transmission. Retention biases must be taken into account during analysis. Run-in designs that delay randomization may improve retention in clinical trials.