Comparing those diagnosed early versus late in their HIV infection: implications for public health

Routine HIV surveillance cannot distinguish between recent and older infections: HIV-positive individuals reported soon or long after infection are both considered new diagnoses from a surveillance perspective, notwithstanding the time since infection. This lack of specificity makes it difficult to understand the jurisdiction-specific trends in HIV epidemiology needed for prevention planning. Previous efforts have been made to discern such timing of infection, but these methodologies are not easily applied in a public health setting. We wished to develop a simple protocol, using routinely collected information, to classify newly diagnosed infections as recent or older, and to enumerate and characterize recent versus older infections. Applying our methodology to a review of HIV cases reported between January 2011 and December 2014, we classified 62% of cases; one-third of these were recent infections. Although men who have sex with men (MSM) and persons from HIV-endemic countries (HEC) disproportionally accounted for new HIV diagnoses, the dynamics of HIV transmission within these groups differed dramatically: MSM accounted for the majority of recent infections, whereas persons from HEC accounted for the majority of older infections. Among older infections, one-quarter were previously unaware of their infection. Categorizing cases in this manner yielded greater, jurisdiction-specific understanding of HIV, and guides subpopulation-specific interventions.