HIV-1 subtypes and differences in heterosexual HIV transmission among HIV-discordant couples in Rakai, Uganda.

OBJECTIVE: To determine whether heterosexual transmission of HIV differs according to HIV-1 subtype.
DESIGN: A retrospective observational cohort.
METHODS: HIV-1 subtype effects on heterosexual HIV-1 transmission were determined among 268 HIV-discordant couples retrospectively identified from a population cohort in Rakai, Uganda. HIV-1 subtype (gag and gp41 sequencing and multiregion hybridization assay) and viral loads (reverse transcriptase PCR) were determined. Adjusted incidence rate ratios (adj IRR) of HIV transmission by subtype were estimated by multivariable Poisson regression adjusting for characteristics of index HIV-positive and HIV-negative partners.
RESULTS: Adjusting for index HIV-positive partners' age, viral load, stage of disease, genital ulcer disease, and HIV-negative partners' genital ulcer disease and nonuse of condoms, subtype A viruses were associated with a higher rate of transmission than subtype D [adj.IRR 1.98, 95% confidence interval (CI) 1.17-3.34], but no differences in transmission were observed between recombinant viruses and subtype D (aIRR 1.53, P = 0.25). Index-positive partners' age less than 30 years (adj.IRR 3.44, 95% CI 1.75-6.78) and viral load (adj.IRR 2.37, 95% CI 1.75-3.21), and index-negative partners' genital ulcer disease (adj.IRR 1.71, 95% CI 1.08-2.70) and nonuse of condoms (adj.IRR 1.94, 95% CI 1.15-3.28) were significant determinants of HIV transmission.
CONCLUSION: In Rakai, Uganda, subtype A viruses have a significantly higher rate of heterosexual transmission than subtype D viruses. Differential subtype transmission efficiency may be important for HIV vaccine evaluation and could contribute to subtype-specific HIV epidemics in sub-Saharan Africa.