Risk factors for negative sputum acid-fast bacilli smears in pulmonary tuberculosis: results from Dakar, Senegal, a city with low HIV seroprevalence

SETTING: Two teaching hospitals in Dakar, Senegal, a West African country w ith a low prevalence of human immunodeficiency virus (HIV) infection. OBJECTIVE: To determine whether patients with HIV-associated pulmonary tube rculosis have fewer acid-fast bacilli (AFB) in their sputum as assessed by routine microscopy, and to correlate the findings with systematically obtai ned clinical, radiographic and laboratory variables. DESIGN: Prospective st udy from November 1995 to October 1996 of 450 consecutive patients diagnose d with pulmonary tuberculosis. RESULTS: Tuberculosis was diagnosed in 380 patients (84.4%) by positive bac teriology, in 61 (13.6%) by a favorable response to anti-tuberculosis chemo therapy, and in nine (2.0%) by the presence of a miliary radiographic patte rn. Forty (8.9%) patients were HIV-seropositive. AFB-negative smears were f ound in 14/40 (35.0%) of the HIV-seropositive patients with pulmonary tuber culosis compared with 71/410 (17.3%) of the seronegative patients (risk rat io [RR] = 2.02, 95% confidence interval [CI] 1.26-3.24, P 0.01). A Multivar iate analysis revealed that AFB smear negativity was associated with absenc e of cavitation (P = 0.002), lack of cough (P 0.005), the presence of HIV s eropositivity (P = 0.02), a CD4+ cell count above 200/mm(3) (P = 0.02), and age over 40 years (P = 0.03). CONCLUSIONS: Compared with HIV-seronegative patients with pulmonary tubercu losis, seropositive patients in Dakar, Senegal, are more likely to have neg ative sputum-AFB smears. This phenomenon has now been observed in seven of eight sub-Saharan African countries with varying HIV seroprevalence from wh ich reports are available.