Vaccine and Infectious Disease Division

Reducing transmission risk by reducing HIV loads in blood

The risk of HIV transmission is strongly associated with the level of HIV-1 RNA in the blood plasma (the viral load) of an infected individual, with greater viral loads associated with greater risks of transmission.  A better understanding of this linkage is needed to improve predictions of the efficacy of antiretroviral therapy (ART) and other interventions, and to model their potential effects on HIV transmission.

As part of the Partners In Prevention HSV/HIV Transmission Study, UW researcher Jairam Lingappa, VIDD member James Hughes, VIDD staff scientist Deborah Donnell, VIDD co-director Lawrence Corey, VIDD affiliate investigator Anna Wald and colleagues performed a prospective study from 2004-2008 of nearly 3400 serodiscordant African couples (where one individual is HIV-positive and the other is not) for over 4000 person-years of study.  In this study, they identified 108 confirmed transmission events from one partner to the other within a couple.  Based on data they also collected about viral load in the transmitting partner, they were able to develop a model predicting transmission risk as a function of viral load, which identified a direct relationship of higher viral loads correlating with higher transmission risks.  Their model predicts that a reduction in viral load of 0.74 log10 copies/ml (roughly equivalent to a five-fold decrease in the amount of circulating virus) will reduce transmission risk by 50%, regardless of the initial viral load.  Therefore, in the context of using ART for prevention of HIV-1 transmission, given a population with a similar distribution of viral loads as seen in the Partners in Prevention clinical trial cohort, targeting ART to the 58% of infected individuals with the highest viral load is predicted to provide 90% of the HIV-1 prevention benefit of targeting all infected individuals.  Thus, HIV-1 prevention strategies could focus on individuals with the highest viral loads in situations where the high cost of ART makes it prohibitive to provide all HIV-infected individuals with ART.  However, further advances and reduction of cost in viral load testing technology would be necessary to make this a realistic goal.

Lingappa JR, Hughes JP, Wang RS, Baeten JM, Celum C, Gray GE, Stevens WS, Donnell D, Campbell MS, Farquhar C, Essex M, Mullins JI, Coombs RW, Rees H, Corey L, Wald A; Partners in Prevention HSV/HIV Transmission Study Team. Estimating the impact of plasma HIV-1 RNA reductions on heterosexual HIV-1 transmission risk. PLoS One. 2010 Sep 13;5(9):e12598.