Using Sexually Transmitted Disease Incidence as a Surrogate Marker for HIV Incidence in Prevention Trials

Abstract

Because many of the sexual behaviors that place individuals at risk of acquiring HIV are the same as those that place them at risk for other sexually transmitted diseases (STDs), researchers and policymakers have called for the use of non-HIV STDs as surrogate markers for HIV infection. This study examined the epidemiologic conditions under which changes in STD incidence are associated with changes in HIV incidence. A mathematical model of HIV/STD transmission was applied to empirical data from a large HIV prevention intervention. The association between participants' HIV infection risk reduction scores and their STD risk reduction scores was measured with use of the Pearson product-moment correlation. The authors examined how the strength of association varied across different epidemiologic parameters and heterosexual behaviors. Moderate to strong associations were noted when the infectivity of the STD was similar to the infectivity of HIV. The association was attenuated for larger STD infectivity values. The prevalence of STD infection was a less important determinant of the strength of association. Stronger associations were obtained when the number of sex partners was large or the number of sex acts was small. Easily transmitted STDs, such as gonorrhea, are unsuitable for general use as surrogate markers for HIV infection. Hepatitis B, syphilis, and chlamydial infection have more promising epidemiologic profiles. Careful studies of STD infectivity are needed to aid in the identification of potential marker STDs.