Combining traditional and molecular epidemiology methods to quantify local HIV transmission among foreign-born residents.

objectivesWe evaluated the ability for molecular epidemiology to augment traditional HIV surveillance beyond the detection of clusters for outbreak investigation. To do this, we address a question of interest to Public Health - Seattle and King County: what proportion of HIV diagnoses among people born outside of the United States are acquired locally?

designKing County residents diagnosed with HIV, 2010-2018.

methodsWe linked HIV-1 pol gene sequences to demographic information obtained from the National HIV Surveillance System, Public Health - Seattle and King County case investigation and partner services interviews. We determined the likely location of HIV acquisition based on HIV testing, travel histories and cluster-based molecular analyses.

resultsAmong 2409 people diagnosed with HIV, 798 (33%) were born outside of the United States. We inferred the location of acquisition for 77% of people born outside of the United States: 26% likely acquired HIV locally in King County (of whom 69% were MSM, 16% heterosexual), and 51% likely acquired HIV outside of King County (primarily outside of the United States). Of this 77% of people for whom we inferred the location of HIV acquisition, 45% were determined using traditional epidemiology methods and an additional 32% were inferred using molecular epidemiology methods.

conclusionWe found that the National HIV Surveillance System misclassified the majority of HIV-infected foreign-born residents as 'new' local infections, and that these cases contribute to an overestimate of local incidence. Our findings highlight how molecular epidemiology can augment traditional HIV surveillance activities and provide useful information to local health jurisdictions beyond molecular cluster detection.