The incidence of tuberculosis in drug users with small tuberculin reaction sizes

SETTING: In persons infected with the human immunodeficiency virus (HIV), a decreased tuberculin reaction cut-point of ≥5 mm induration is recommended.

OBJECTIVE: To determine tuberculosis risk in non-anergic HIV-infected persons with 5–9 mm tuberculin reactions.

DESIGN: A prospective study with semi-annual tuberculin and anergy testing, HIV antibody and T cell subset assays, and active surveillance for tuberculosis.

RESULTS: Participants were 572 HIV-seronegative and 241 HIV-seropositive non-anergic drug users. No tuberculosis occurred in HIV-seronegative persons. Tuberculosis incidence among HIV-seropositive drug users was 3.3, 7.7, 0, and 0.34 per 100 person-years in those with tuberculin reaction sizes of ≥10 mm, 5–9 mm, 1–4 mm, and 0 mm, respectively, and was significantly increased in persons with 5–9 mm induration compared with those with 0–4 mm induration (rate ratio 27.7, 95%CI 2.9–268). Among persons with reaction sizes of 5–9 mm, tuberculosis occurred exclusively in those with CD41 lymphocyte counts <500/mm³ at the time of their 5–9 mm tuberculin reactions.

CONCLUSION: HIV-infected persons with tuberculin reaction sizes of 5–9 mm are at increased risk for tuberculosis compared to non-anergic persons with smaller (0–4 mm) reaction sizes. However, this increased risk may be limited to those with low CD41 lymphocyte counts at the time of tuberculin testing.