Who infects whom? HIV-1 concordance and discordance among migrant and non-migrant couples in South Africa.

OBJECTIVES To measure HIV-1 discordance among migrant and non-migrant men and their rural partners, and to estimate the relative risk of infection from inside versus outside primary relationships. DESIGN A cross-sectional behavioural and HIV-1 seroprevalence survey among 168 couples in which the male partner either a migrant, or not. METHODS A detailed questionnaire was administered and blood was collected for laboratory analysis. A mathematical model was developed to estimate the relative risk of infection from inside versus from outside regular relationships. RESULTS A total of 70% (117 of 168) of couples were negatively concordant for HIV, 9% (16 of 168) were positively concordant and 21% (35 of 168) were discordant. Migrant couples were more likely than non-migrant couples to have one or both partners infected [35 versus 19%; P = 0.026; odds ratio (OR) = 2.28] and to be HIV-1 discordant (27 versus 15%; P = 0.066; OR = 2.06). In 71.4% of discordant couples, the male was the infected partner; this did not differ by migration status. In the mathematical model, migrant men were 26 times more likely to be infected from outside their regular relationships than from inside [relative risk (RR) = 26.3; P = 0.000]; non-migrant men were 10 times more likely to be infected from outside their regular relationships than inside (RR = 10.5; P = 0.00003). CONCLUSIONS Migration continues to play an important role in the spread of HIV-1 in South Africa. The direction of spread of the epidemic is not only from returning migrant men to their rural partners, but also from women to their migrant partners. Prevention efforts will need to target both migrant men and women who remain at home.