• To estimate the percentage of HIV-infected individuals who demonstrate the booster effect [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  

• To determine the relationships among the booster effect, CD4+ cell count, and other HIV-related patient characteristics [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  
• To determine the relationship of boosting to CD4+ cell counts, HIV exposure categories, demographics, and TB risk categories [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  
• To determine the relationship of induration size after the first PPD skin test to that after the second PPD skin test [ Time Frame: After the second PPD skin test ] [ Designated as safety issue: No ]
  

The accuracy of skin testing to detect Mycobacterium tuberculosis (MTb) infection is dependent upon the host's ability to mount a delayed-type hypersensitivity (DTH) reaction; however, the DTH response may be impaired or absent in patients with impaired cell-mediated immunity, a classic characteristic of HIV infection. Patients in whom immunity is diminished, but not absent, may test negative the first time a purified protein derivative skin test for MTb is administered, but if the same skin test is repeated, a positive DTH response may then be elicited. This occurrence is known as the "booster" phenomenon.

Patients who have had a negative purified protein derivative (PPD) skin test for M. tuberculosis within 7-28 days prior to study entry will receive a second PPD test by the Mantoux method (5 TU intradermally to the volar aspect of the forearm). Skin tests will be read 48-72 hours after application.

Patients with a positive skin test (defined as an induration, or small hard knot, of 5 mm or greater forming beneath the skin) will be referred to their primary physicians for further evaluation.