Tuberculosis screening and anergy in a homeless population.

Background: Tuberculosis has again emerged as a growing public health concern in the United States. Among the homeless population, increased risk factors contribute to immunodeficiency, which can cause false-negative results on purified protein derivative (tuberculin) (PPD) skin testing, the standard screening procedure for tuberculosis in individuals. We evaluated the accuracy of PPD skin test results by determining anergy status of patients when offering the PPD test.

Methods: A consecutive convenience sample of 105 underserved men and women were tested at a health clinic located in a homeless shelter in Yonkers, NY. These persons were currently homeless, living in a shelter, or formerly homeless and using the soup kitchen at the shelter. Three antigens, candidin, mumps, and trichophytin, in addition to PPD, were administered intradermally using the Mantoux method, and results were read 48 to 72 hours later on the 100 (95 percent) who returned. An individual was considered to be anergic if the delayed-type hypersensitivity reactions were less than or equal to 2 mm for each of the four antigens.

Results: Of the 100 persons who returned for follow-up, 5 (5 percent) were found to be anergic. Of these 5, all were previously known to be positive for human immunodeficiency virus (HIV).

Conclusions: PPD testing alone was found to be an accurate screening test in this population except in those who were HIV positive.