Redefining the growth of the heterosexual HIV/AIDS epidemic in Chicago

A dramatic shift in the relative distribution of the five categories of heterosexual transmission for AIDS cases diagnosed in Chicago since 1991 prompted a mode-of-transmission validation study of what had become the most frequently reported heterosexual exposure: heterosexual relations with a person with AIDS (PWA) or documented HIV infection whose risk is not specified.

For 395 cases with originally reported heterosexual exposure, one or more of three supplemental data sources were employed: medical records were reviewed, medical providers were interviewed, and patients or proxies (i.e., spouse, significant other, or family member) were interviewed when possible. When reported HIV exposure could not be validated or reclassified, the transmission category employed was "no identifiable risk" (NIR).

Eighty-five percent (336 of 395 cases) were reclassified into different transmission categories. Most notably, 69% (272 of 395 cases) were reclassified into transmission categories that did not involve heterosexual contact, including NIR. The cumulative percentage of cases attributable to heterosexual contact declined from 8% to 5% as a result of reclassification. Additionally, reclassification resulted in a reduction of nearly 50% in the number of AIDS cases attributable to heterosexual contact diagnosed in 1993 and 1994.

In Chicago, an emerging problem in AIDS surveillance appears to be the use of an ambiguous heterosexual exposure category as a default when other information is not readily available. This study has found the growth in AIDS cases among persons exposed to HIV through heterosexual contact to be much slower than previously perceived. This finding may have important implications for the national debate over the extent to which heterosexual people are being infected and how funding and prevention strategies should be prioritized.