Two-step tuberculin skin testing in HIV-infected persons in Uganda

Identifying persons infected with both human immunodeficiency virus (HIV) and Mycobacterium tuberculosis (MTB) is often difficult because of the reduced sensitivity of tuberculin skin testing in HIV-infected persons. To determine the value of two-step tuberculin skin testing (TTST) as a method of increasing the sensitivity of tuberculin skin testing in HIV-infected persons, a consecutive sample of 58 HIV-infected persons being screened for a TB preventive therapy trial in Uganda with an initial purified protein derivative (PPD) response <5 mm completed two-step tuberculin and candida skin testing. The mean change in PPD size between the two tests, placed a mean of 8 d apart, was +2.1 mm (SD 4.4 mm, range -4 to +16 mm). Seventeen subjects (29%) had a boosted response (PPD₁ <5 and PPD₂ ≤ 5). In a multiple logistic regression model, boosted responses were independently associated with a CD4 count between 200 and 500 μl^-1 (p = 0.02) and a higher body mass index (p = 0.05). TTST may be valuable in identifying MTB infection and in preventing misclassification of boosted responses as skin test conversions in HIV-infected persons, especially persons with CD4 counts between 200 and 500 μl^-1 from areas with a high prevalence of MTB infection or from areas with a low prevalence of MTB infection who have other risk factors for MTB infection.