Previously undiagnosed HIV infections identified through cluster investigation, North Carolina, 2002-2007.

During cluster investigation, index patients name social contacts that are not sex or drug-sharing partners. The likelihood of identifying new HIV infections among social contacts is unknown. We hypothesized greater odds of identifying new infections among social contacts identified by men who report sex with men (MSM). We reviewed North Carolina HIV diagnoses during 2002-2005 and used logistic regression to compare testing results among social contacts of MSM, men who report sex with women only (MSW) and women. HIV was newly diagnosed among 54/601 (9.0 %) social contacts tested named by MSM, 16/522 (3.1 %) named by MSW, and 23/639 (3.6 %) named by women. Compared with those named by MSW, odds of new HIV diagnosis were greater among MSM social contacts (adjusted odds ratio: 2.5; 95 % confidence interval: 1.3-4.7). Testing social contacts identified previously undiagnosed HIV infections and could provide an opportunity to interrupt transmission.