FACTORS AFFECTING THE YIELD OF ACID-FAST SPUTUM SMEARS IN PATIENTS WITH HIV AND TUBERCULOSIS

Objective: To evaluate the sensitivity of acid-fast sputum smears in the diagnosis of pulmonary Mycobacterium tuberculosis (MTB). Design: Retrospective chart and radiographic film review. Setting: Department of Veterans Affairs Medical Center in New York City. Patients: All patients with positive sputum cultures for MTB during 1989 to 1991, including 100 with HIV, and 76 without HIV infection. Parameters: The likelihood of a positive acid-fast sputum smear, related to chest radiograph findings, CD4 cell counts, drug sensitivity, and the presence of disseminated disease. Results: Overall, 60 percent of patients with HIV had positive acid-fast smears, compared with 57 percent of non-HIV-infected patients. A relative absence of cavitary infiltrates did not substantially reduce the frequency of acid-fast smears in patients with and without HIV. Patients with HIV and CD4 count <50, 50 to 200, and >200 had positive acid-fast smear rates of 58 percent, 60 percent, and 58 percent, respectively; HIV-infected patients with drug-resistant organisms had 65 percent positive smears. Smear positivity was 96 percent in patients with HIV infection and disseminated MTB. Conclusions: Positive acid-fast sputum smears in culture-proven MTB occur with similar frequency in patients with and without HIV. The absence of cavitary disease did not significantly reduce the frequency of positive acid-fast smears. For patients with HIV, the likelihood of a positive smear was also independent of CD4 cell counts and drug resistance. Patients with HIV and disseminated MTB had positive sputum smears in nearly all cases.