Factors Affecting the Yield of Acid-fast Sputum Smears in Patients With HIV and Tuberculosis

Abstract

To evaluate the sensitivity of acid-fast sputum smears in the diagnosis of pulmonary Mycobacterium tuberculosis (MTB). Retrospective chart and radiographic film review. Department of Veterans Affairs Medical Center in New York City. All patients with positive sputum cultures for MTB during 1989 to 1991, including 100 with HIV, and 76 without HIV infection. 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. 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 56 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.