Underestimation of Mycobacterium tuberculosis infection in HIV-infected subjects using reactivity to tuberculin and anergy panel

Background This study aimed to evaluate purified protein derivative (PPD) r eactivity and its interrelationship with anergy panel and CD4+ lymphocytes in HIV-infected subjects as compared to PPD reactivity in HIV-uninfected in dividuals in a tuberculosis endemic and high Bacillus Calmette-Guerin (BCG) coverage environment. Methods Clients of four Mexico City HN detection centres were screened for HIV-1 antibodies (ELISA or haemagglutination, Western Blot); reactivity to PPD (Mantoux PPD, 5TU RT-23), Candida (1:1000, 0.1 ml), and tetanus toroid (10Lf, 0.1 ml); and CD4+ T cells. Active tuberculosis was excluded. Informe d consent was obtained. Results From 5130 clients 1168 subjects were enrolled; of these 801 (68.6%) were HN positive. Reactivity to PPD among HIV-positive subjects was found in 174 (22%), 261 (32.6%), and 296 (37%), at PPD cutoff levels of greater t han or equal to 10 mm, greater than or equal to 5 mm, and greater than or e qual to 2 mm as compared to 224 (61%) of 367 HIV-negative individuals' reac tors to PPD (greater than or equal to 10 mm) (P < 0.001). After exclusion o f anergic individuals using two cutoff levels for cutaneous allergens (less than or equal to 2 mm and less than or equal to 5 mm), PPD reactivity betw een HIV-infected and uninfected individuals continued to be significantly d ifferent. Only HIV-infected individuals with CD4+ T cells greater than or e qual to 500 cells/mm(3) had similar reactivity to PPD as HIV-uninfected ind ividuals. Variables associated with PPD reactivity were CD4+ T cell counts, BCG scar, HIV infection and age. Conclusions PPD reactivity was useful to diagnose tuberculosis infection on ly among HIV- infected individuals with CD4+ counts greater than or equal t o 500 cells/mm(3). Among individuals with lower counts, lowering cutoff lev els or using anergy panel did not permit comparable reactivity as that obse rved among HIV-uninfected individuals.