HIV-1 discordant couples in Karnataka, South India: is the sex ratio of index cases changing?

India has an estimated 2.5 million HIV infections, most of which are heterosexually transmitted. Women comprise 40% of infected adults. In India, 90% of women between the ages of 15 and 45 years are married. Previous literature has suggested that sexual intercourse with an HIV-infected husband represents a married woman's greatest risk for being infected. However, a recent meta-analysis of discordant couples from sub-Saharan Africa reported that women were the index case in half of all couples. Similar data are not available from India. This cross-sectional study describes the epidemiology of 925 discordant couples from five districts in Karnataka province, one of the high HIV prevalence provinces in India. Men were the index case in 74% of couples. However, in young couples (where the index case was aged <30 years), women were more likely to be the infected partner (64% of couples). Condom use was reported by 46% of these discordant couples. These results suggest an emerging predominance of female index case infections among younger discordant couples in India, and point to the need for focusing HIV preventive messages on youth and couples before marriage.