Do people who develop AIDS within 12 months of HIV diagnosis delay HIV testing?

Individuals diagnosed with AIDS within 12 months of HIV diagnosis have been considered "late testers." Prevalence estimates of late testers have been made using HIV/AIDS surveillance data, and high rates of late testing have been reported. However, studies evaluating this definition have not been conducted. We measured the degree of misclassification of delayed testing based on this surveillance definition of late testing.

We used dates of negative HIV tests among people who met this definition of late testing in San Francisco from 2007 to 2008 to reclassify people as "verified non-late testers" if there was a negative HIV test within five years of HIV diagnosis, as "verified late testers" if there were no prior tests or if negative tests were recorded five or more years prior to diagnosis, or as "late-tester status not verified." We measured misclassification of late-tester status and the prevalence of late testing using the different definitions of late testing.

Of the 270 people who developed AIDS within 12 months of HIV diagnosis, we found that 89 (33.0%) were verified late testers, 131 (48.5%) were verified non-late testers, and 50 (18.5%) were unverifiable. Using the surveillance definition (individuals who develop AIDS within 12 months of HIV diagnosis), the prevalence of late testing was 26.3%, whereas it was 9.0% when restricted to individuals verified as late testers.

Defining people who develop AIDS within 12 months of HIV diagnosis without taking into consideration the dates of prior negative HIV tests leads to substantial misclassification of late testing.