Browsing by Author "Li, Xianbin"

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    Probability of HIV-1 transmission per coital act in monogamous, heterosexual, HIV-1-discordant couples in Rakai, Uganda
    (The Lancet, 2001) Gray, Ronald H.; Wawer, Maria J.; Brookmeyer, Ron; Sewankambo, Nelson K.; Serwadda, David; Wabwire-Mangen, Fred; Lutalo, Tom; Li, Xianbin; vanCott, Thomas; Quinn, Thomas C.
    The probability of HIV-1 transmission per coital act in representative African populations is unknown. We aimed to calculate this probability overall, and to estimate how it is affected by various factors thought to influence infectivity. Methods 174 monogamous couples, in which one partner was HIV-1 positive, were retrospectively identified from a population cohort in Rakai, Uganda. Frequency of intercourse and reliability of reporting within couples was assessed prospectively. HIV-1 seroconversion was determined in the uninfected partners, and HIV-1 viral load was measured in the infected partners. Adjusted rate ratios of transmission per coital act were estimated by Poisson regression. Probabilities of transmission per act were estimated by log-log binomial regression for quartiles of age and HIV-1 viral load, and for symptoms or diagnoses of sexually transmitted diseases (STDs) in the HIV-1-infected partners. Results The mean frequency of intercourse was 8·9 per month, which declined with age and HIV-1 viral load. Members of couples reported similar frequencies of intercourse. The overall unadjusted probability of HIV-1 transmission per coital act was 0·0011 (95% CI 0·0008–0·0015). Transmission probabilities increased from 0·0001 per act at viral loads of less than 1700 copies/mL to 0·0023 per act at 38 500 copies/mL or more (p=0·002), and were 0·0041 with genital ulceration versus 0·0011 without (p=0·02). Transmission probabilities per act did not differ significantly by HIV-1 subtypes A and D, sex, STDs, or symptoms of discharge or dysuria in the HIV-1-positive partner.
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    Stochastic simulation of the impact of antiretroviral therapy and HIV vaccines on HIV transmission; Rakai, Uganda
    (Aids, 2003) Gray, Ronald H.; Li, Xianbin; Wawer, Maria J.; Gange, Stephen J.; Serwadda, David; Sewankambo, Nelson K.; Moore, Richard; Wabwire-Mangen, Fred; Lutalo, Tom; Quinn, Thomas C.
    To model the effects of antiretroviral therapy (ART) and HIV vaccines on HIV transmission using empirical data from studies in Rakai, Uganda. Design: A stochastic simulation model estimated HIV incidence, probabilities of transmission per coital act and the reproductive number (R0) with ART and HIV vaccines. Model inputs included Rakai data on HIV transmission probabilities per coital act by HIV viral load, age and gender, and sexual behaviors. The impacts of therapy were derived from US programs, and vaccine assumptions included preventive efficacies ranging from 25 to 75%. Component projection models estimated the numbers of HIV-infected persons over 20 years. Results: The model incidence [1.57/100 person years (PY)] closely fitted empirical data (1.5/100 PY). Simulations of ART using DHHS treatment guidelines, predicted declines in HIV incidence, but R0 remained . 1.0, and the numbers of HIV-positive persons did not change substantially over 20 years. Preventive vaccines with . 50% efficacy and . 50% population coverage could reduce R0 to , 1.0, and substantially reduce the number of HIV-infected persons over 20 years. Concurrent ART and a preventive vaccine can have substantial impact at lower levels of population coverage and would markedly reduce the HIV infected population over 20 years. However, behavioral disinhibition with increased numbers of sexual partners in either ART or vaccine recipients, increased HIV incidence and diminished intervention impact. Conclusion: ART alone cannot control the HIV epidemic in mature epidemics such as Rakai, and persons in need of therapy will increase over time. ART in combination with a low efficacy vaccine could control the epidemic, if behavioral disinhibition is prevented.