Background:  Infection with sexually transmitted diseases (STD) increases risk of HIV transmission. Few studies in the United States have examined public health surveillance data for risk factors associated with newly diagnosed HIV in patients with concomitant STD. We evaluated Illinois and Chicago Departments of Public Health surveillance databases to determine risk factors associated with infection of STD (Chlamydia, gonorrhea, or early syphilis) and newly diagnosed HIV.
Methods:  Test results for Chlamydia, gonorrhea, early syphilis (primary, secondary, and early latent), and HIV from clinics in Illinois in 2002 reporting client information to public health surveillance databases were merged with demographic and behavioral survey data collected during client visits. STD was defined as any positive non-HIV result. Multivariate analysis was performed to assess factors associated with laboratory-confirmed STD and newly diagnosed HIV co-infection.
Results:  Among 43,517 client encounters in which specimens were collected concomitantly for STD and HIV tests, 5814 (13.4%) had positive STD test results. There were 308 (0.7%) positive new HIV test results, of which 71 (23.1%) had concomitant infection with an STD. Detection of any STD was associated with increased risk (OR 1.9, 95%CI 1.5 to 2.5) of newly recognized HIV infection. Compared to STD⁺, HIV^– cases, age >30 years (OR 1.9, 95%CI 1.0 to 4.4), homosexual male (OR 22.2, 95%CI 11.3 to 43.7), and bisexual male (OR 22.4, 95%CI 7.8 to 64.8) were independent risk factors for STD and HIV co-infection. Among distinct STD, syphilis (n = 438) was the most infrequent (7.5%), but was reported in the highest proportion (10.1%, n = 31) of new HIV⁺ cases and conferred the greatest risk (OR 11.0, 95%CI 7.7 to 15.8) for newly recognized HIV seroconversion. 
Conclusions:  Active STD were common among persons newly diagnosed with HIV at public health clinics. Men who have sex with men (MSM) were at increased risk for newly diagnosed HIV with STD co-infection. Persons with a concomitant STD and HIV were older than US populations that generally constitute the greatest proportion STD cases. These results from a large statewide database highlight the role in particular of syphilis among populations at high risk for HIV transmission. Public health interventions targeting MSM and older adults for effective testing and prevention strategies are critically needed within high-risk networks for transmission of STD and HIV.