HIV serodiscordant couples in stable relationships are not usually the target of public health interventions for reduction of HIV transmission. Nevertheless, these couples benefit from ongoing counseling and testing. Studies have demonstrated that systematic efforts to identify serodiscordant couples in stable relationships have an impact on HIV transmission and may increase antiretroviral adherence.12,13 In the present cohort, the majority of HIV-1 infected index cases in serodiscordant relationships were women who acquired infection through unprotected sexual activity and were identified during regular prenatal care, a common feature in many settings.14 In men, acquisition of HIV-1 infection through IDU occurred in similar proportions as acquisition of infection through sexual intercourse. ARV use was much more frequently initiated for MTCT purposes than for a low CD4 count or disease progression in our study. Although it was not possible to correlate an STD diagnosis with an HIV transmission event, a high incidence of STDs (23.6%) was observed in our patients.
Although we could not find a correlation between condom use and heterosexual HIV transmission, it is interesting to note that all couples reporting no condom use were serodiscordant couples with a female index case, whereas couples with male index cases reported consistent practice of safe sex. Despite these reports, 4 male index patients transmitted infection to their partners, and in 1 of these cases, pregnancy also occurred. Thus it is debatable whether condom use was truly consistent. The timing of seroconversion was associated with development of pregnancy in half of our seroconversion cases. This suggests that the desire to have children may influence risk taking behaviors in serodiscordant couples. Other studies of serodiscordant couples have reported a high rate of unsafe sexual practices among individuals in stable relationships.15 Among uninfected women in such relationships, seroconversion during pregnancy is a major risk factor for HIV-1 transmission to the infant.16 Nevertheless, the rate of transmission seems to vary by geographic area, with a very low HIV incidence observed among serodiscordant couples in Pune, India,17 as opposed to African cohorts from Uganda, Tanzania, and Zambia2,18–20. These findings may be due to differences in condom use across cohorts, and variations in median CD4 cell counts, the magnitude of virus load, duration of the observation period, and rate of STIs.
In our study, heterosexual transmission occurred more frequently from an HIV infected male to a female (15% vs. 3% transmission). This difference was not statistically significant likely because of our small sample size, a limitation of this study. Studies conducted in North America and Europe demonstrated higher transmission rates from men to women.21,22 However, other studies in large African cohorts have shown the opposite, with a higher efficiency of HIV sexual transmission from female to male partners.1,2 Others have not found a statistically significant difference in sexual HIV transmission risk by gender.23 It seems that the most important predictor of transmission is the magnitude of the virus load, a risk factor of greater significance than patient gender.23 In studies conducted in Uganda, virus load was significantly associated with HIV transmission and much more frequently elevated among individuals in seroconcordant couples than infected individuals in serodiscordant relationships.24 HIV transmission seems to occur as a function of virus load in serum, semen, and genital secretions.2,25 With the widespread use of ARVs, transmission events seem to have been drastically reduced in the HAART era.4,6 In our cohort, we did not observe any transmission events in patients receiving ARVs or with undetectable virus loads.
Our data suggests a possible protective role of ARV use in the prevention of HIV-1 heterosexual transmission between sexual partners who are HIV-1 serodiscordant. Large randomized clinical studies evaluating the role of ARV in prevention of sexual transmission of HIV-1 infection are ongoing and should further elucidate the role of virus load and multiple additional risk factors involved in the pathogenesis of HIV-1 transmission.
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