Most positive HIV western blot tests do not diagnose new cases in New York City: implications for HIV testing programs.

OBJECTIVE: To evaluate HIV testing efforts based on surveillance data.
METHODS: We determined the contribution of new diagnoses to all positive confidential HIV-1 Western blotting conducted in New York City between 2004 and 2006 based on clinical history recorded in the HIV Surveillance Registry, by testing site type.
RESULTS: Of 31,504 positive Western blots reported and linked to Registry cases, 36.8% were new diagnoses and 63.2% were repeat positive tests. City health department clinics and private physicians' offices reported greater proportions of new diagnoses than other testing sites (64.4% and 58.3% vs. 31.1%). The percentage of positive tests at health department clinics that were new diagnoses increased from 59.8% in 2004 to 69.0% in 2006 (P = 0.001), coinciding with efforts to expand HIV testing. Repeat positive testers were significantly older, more likely to have an injection drug use history or AIDS, and less likely to be foreign-born.
CONCLUSIONS: Repeat testing of known HIV-infected persons is common and an inefficient use of HIV prevention resources when the purpose of testing is to diagnose previously unidentified infections. Initiatives to increase HIV testing should be evaluated routinely using surveillance data to determine the proportion of infected persons identified who are newly diagnosed.