HIV Viral load

The impact of viral load in relation to other risk factors for heterosexual transmission of HIV has been studied in a study of 415 Ugandan couples with discordant HIV serostatus. Along a 30 months follow-up period, 90 patients seroconverted (21.7 percent). The following was learned:

  • The efficiency of transmission is about the same for female to male as male to females.
  • The mean viral load was much higher in those who transmitted HIV to their partner (90,254 vs. 38,029 RNA copies per ml). In addition, viral RNA loads less than 1500 copies per ml caused no cases of transmission in regarding to 51 patients.
  • A dose/response relationship defines increased transmission with viral load. In multivariate analysis, each log increment in viral load was linked to a rate ratio of 2.45 for seroconversion.

The importance of viral load is also underscored by mathematical models that suggest that a large proportion of HIV infections may be transmitted by individuals with primary infection. This is probably related to the high levels of viremia that are seen in the setting of acute infection.

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John G Barlett, Martin S Hirsch, Barbara H McGovern. The stages and natural history of HIV infection. UpToDate. <> Accessed: 7/8/2012.