Two-step tuberculin skin testing of injection drug users recruited from community-based settings

SETTING: Cross-sectional study of drug users recruited from street-based settings in four US cities: Denver, Portland, Oakland and San Francisco. OBJECTIVE: To evaluate responses to two-step tuberculin skin testing among HIV-positive and HIV-negative injection drug users. DESIGN: Subjects were recruited from existing studies of HIV and risk behaviors for tuberculin skin testing. Those with a negative initial tuberculin test were referred for a second skin test 1-3 weeks later. A positive tuberculin test was defined as ≥10 mm, or ≥5 mm if the subject was HIV-positive. RESULTS: Of 997 persons receiving an initial tuberculin test, 13% had a positive response. Of 644 persons receiving a second tuberculin test, 8% had a positive response, with rates as high as 14% among those from Oakland and 12% among African Americans. HIV-positive subjects were less likely to have skin test responses ≥10 mm on the initial test (P = 0.03), or increases between the initial and second test of ≥10 mm (P = 0.06). CONCLUSION: Boosting occurred in both HIV-positive and HIV-negative injection drug users. Two-step testing should be considered for this population, particularly those on whom repeat tuberculin testing will be performed.