Rates of HIV-1 Transmission Per Coital Act, by Stage of HIV-1 Infection, in Rakai, Uganda
May 2, 2005
In this retrospective study, researchers identified 235 monogamous HIV-discordant couples in a Rakai, Uganda, population-based cohort to estimate rates of HIV transmission per coital act (PCA) and stage of infection. Transmission within pairs was confirmed by sequence analysis. Rates of transmission PCA were estimated by index partner's stage of infection (recent seroconversion, prevalent or late-stage infection). The adjusted rate ratio was estimated by multivariate Poisson regression.Adapted from:
The average coital act frequency was 10.2/month (median = 8.3/month) among couples with an incident index partner and 10.0/month among couples with a prevalent index partner. Coital frequency declined from an average 8.7/month to 6.2/month before the death of an index partner. Median viral load approximately five months after seroconversion was 30,000 copies/mL; and a median 2,600 copies/mL by 15 months. Median viral load among prevalent partners increased from 10,300 copies/mL at baseline to 15,000 copies/mL after 30 months of follow-up. Among late-stage partners, median viral load was 112,600 copies/mL at the last test date, conducted an average five months before death.
Of the 235 couples, 68 (28.9 percent) index partners transmitted HIV to their previously uninfected partners. Transmission was highest among 23 incident partners, of whom 10 (43.4 percent) transmitted HIV to their partners within approximately 2.5 months after seroconversion, and 13 (56.5 percent) had after approximately 35 months. Prevalent index partners transmitted infection at a mean annual rate of 8.4 percent. And of 51 late-stage partners, 19 (37.3 percent) transmitted HIV within approximately 6-35 months before death.
The overall average rate of HIV transmission PCA was 0.0012; 0.0082 PCA within approximately 2.5 months after the index partner's seroconversion; 0.0015 PCA 6-15 months after seroconversion; 0.0007 PCA among HIV-prevalent index partners; and 0.0028 PCA 6-25 months before the index partner's death.
Higher transmission rates were significantly associated with early and late stage of HIV infection, viral load of 3.50 log10 copies/mL or more, genital ulcer disease, and younger age (15-29 years) of index partner.
"After seroconversion of the index partner, the rate of transmission (0.0082/coital act) within the first 2.5 months was almost 12-fold higher than that observed in prevalent index couples (0.0007/coital act)," concluded authors. The authors acknowledged that they were unable to determine the magnitude or duration of peak viremia or HIV transmission PCA during the weeks immediately following seroconversion, but viral loads were consistent with levels seen approximately five months after incident partners' seroconversion. They noted that a recent Malawi study suggested a peak HIV load of 6.10 log10 copies/mL (more than 1 million RNA copies/mL) shortly after HIV acquisition. For Rakai couples, if the length of exposure between incident infection and transmission was only 1 month (approximately 10 coital acts) instead of the study's estimated 2.5 months, the rate of transmission could possibly be very high, as much as 0.02/coital act among incident partners, they said.
"The highest rate of transmission per coital act, as well as the highest proportion of transmissions, occurred during early-stage infection in index partners, a time when few seroconverters know their HIV status or receive ART," noted the authors. The overall contribution of late-stage infection to the heterosexual epidemic "is likely to be limited, because individuals with advanced HIV infection report less sexual intercourse and have fewer partners, and only a minority of couples remain discordant by this stage." Initiating ART to late-stage patients, under current guidelines, "may have only a modest impact on HIV transmission." "Measures that prevent primary HIV infection or reduce early viremia (as may occur with HIV vaccines) are likely to have a greater effect than ART on the spread of HIV. Increased efforts to identify persons with early-stage HIV infection are also warranted, to promote safe behaviors, and, where appropriate, to provide ART."
Journal of Infectious Diseases
05.01.05; 191(9):1403-9; Maria J. Wawer; Ronald H. Gray; Nelson K. Sewankambo; David Serwadda; Xianbin Li; Oliver Laeyendecker; Noah Kiwanuka; Godfrey Kigozi; Mohammed Kiddugavu; Thomas Lutalo; Fred Nalugoda; Fred Wabwire-Mangen; Mary P. Meehan; Thomas C. Quinn
This article was provided by CDC National Prevention Information Network. It is a part of the publication CDC HIV/Hepatitis/STD/TB Prevention News Update.