Factors affecting the yield of acid-fast sputum smears in patients with HIV and tuberculosis.

Abstract

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 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.