Factors associated with tuberculin skin test reactivity among HIV-infected people in Bangkok.

INH preventive therapy (IPT) has been shown in several randomized controlled trials to reduce the risk of developing active TB in tuberculin skin test (TST) or purified protein derivative (PPD) positive HIV infected individuals. Detection of latent tuberculosis by TST and determination of factors associated with the PPD positivity in HIV-infected persons are important for the targeting of chemoprophylaxis. Six hundred asymptomatic and early symptomatic HIV-infected subjects attending the AIDS Clinic of the Chulalongkorn University Hospital, Bangkok, Thailand were enrolled in two randomized clinical trials of chemoprophylaxis against TB from December 1994 to December 1996. The availability of baseline characteristics, including TST reactivity, among these participants enabled a cross-sectional analysis of factors associated with PPD positivity. The results showed that 117 (19.5%) were PPD positive and 483 (80.5%) were PPD negative with ages 18-65 years (median 29 years). HIV exposure category was 46.2%, 34.5%, and 6.7% for heterosexual contact, commercial sex work, and homosexual and bisexual male contact respectively. The median CD4 cell count was 315/mm3 (range, 5-1,074/mm3). HIV exposure category and CD4 cell count were significantly associated with PPD status. Homosexual/bisexual contact had 3 times higher risk of PPD positivity than heterosexual contact (adjusted OR=2.9; 95% CI, 1.4-6.1) and risk of PPD positivity was higher among patients with CD4 cell counts of 200-500/ mm3 (adjusted OR=1.8; 95% CI, 1.0-3.1) and above 500/mm3 (adjusted OR=3.4; 95% CI, 1.7-6.7) when compared to patients with CD4 cell counts of less than 200/mm3. The HIV-infected persons in Bangkok with homosexual/bisexual contact are at higher risk for latent TB. Population-based tuberculin screening without accompanying HIV testing cannot be used to estimate the prevalence of actual latent TB in a population where HIV infection is widespread, such as in Thailand.