Background: It is unclear whether there are differences between men and women with human immunodeficiency virus type 1 (HIV-1) infection in the plasma level of viral RNA (the viral load). In men, the initial viral load after seroconversion predicts the likelihood of progression to the acquired immunodeficiency syndrome (AIDS), but the relation between the two has not been assessed in women. Currently, the guidelines for initiating antiretroviral therapy are applied uniformly to women and men. Methods: From 1988 through 1998, the viral load and the CD4+ lymphocyte count were measured approximately every six months in 156 male and 46 female injection-drug users who were followed prospectively after HIV-1 seroconversion. Results: The median initial viral load was 50,766 copies of HIV-1 RNA per milliliter in the men but only 15,103 copies per milliliter in the women (P<0.001). The median initial CD4+ count did not differ significantly according to sex (659 and 672 cells per cubic millimeter, respectively). HIV-1 infection progressed to AIDS in 29 men and 15 women, and the risk of progression did not differ significantly according to sex. For each increase of 1 log in the viral load (on a base 10 scale), the hazard ratio for progression to AIDS was 1.55 (95 percent confidence interval, 0.97 to 2.47) among the men and 1.43 (95 percent confidence interval, 0.76 to 2.69) among the women. The median initial viral load was 77,822 HIV-1 RNA copies per milliliter in the men in whom AIDS developed and 40,634 copies per milliliter in the men in whom it did not; the corresponding values in the women were 17,149 and 12,043 copies per milliliter. Given the recommendation that treatment should be initiated when the viral load reaches 20,000 copies per milliliter, 74 percent of the men but only 37 percent of the women in our study would have been eligible for therapy at the first visit after seroconversion (P<0.001). Conclusions: Although the initial level of HIV-1 RNA was lower in women than in men, the rates of progression to AIDS were similar. Treatment guidelines that are based on the viral load, rather than the CD4+ lymphocyte count, will lead to differences in eligibility for antiretroviral treatment according to sex.
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