Surveillance for incident HIV infection: New technology and new opportunities

Although surveillance for HIV infection has traditionally focused on the in cidence of AIDS and the prevalence of HIV, new diagnostic technologies that allow the estimation of incident HIV infection have become available. Numb er and distribution of new cases of HIV infection, rather than old cases, a re the data most relevant to guide rational application of HIV prevention p rograms. Historically, incident HIV infection has been measured in longitud inal cohort studies, diagnosed clinically or since 1993 by detection of ser oconverting patients (during the window period before appearance of HIV ant ibody) who are viremic as measured by p24 antigen or RNA-PCR. The sensitive -less sensitive EIA test (or serologic testing algorithm for recent HIV ser oconversion [STAHRS]) has now made the serologic diagnosis of incident HIV infection in individual patients as well as the estimation of HIV incidence in populations possible. Examples of the public health application of this are studies of HIV incidence in anonymous test site attendees, sexually tr ansmitted disease clinic patients, and in-treatment injection drug users in San Francisco. These sorts of studies allow us not only to measure inciden ce cross-sectionally but also facilitate surveillance for HIV subtypes and primary antiretroviral resistance, targeting early antiretroviral therapy a nd partner notification, and understanding who is "failing" prevention. Hav ing an HIV surveillance system that focuses on incident rather than prevale nt infection should be our long-term goal.