[Determination of risk factors of smear-negative pulmonary tuberculosis]

to compare the epidemiological, clinical and paraclinical features of smear-negative pulmonary tuberculosis (PT-) and the smear-positive pulmonary tuberculosis (PT+), to determine the risk factors of smear-negative pulmonary tuberculosis.

It was a prospective study, conducted from November 1995 to November 1996. Data were analysed by EPI-INFO 6.04 (OMS/CDC).

The study included 426 patients with pulmonary tuberculosis. Among them, 348 (81.7%) were PT+ and 78 (18.3%) were PT-. The sex-ratio was 2.4. Age group of 26 to 45 years was more affected (58.4% for the PT+ and 52.6% for the PT-). The prevalence of HIV infection was statistically higher in PT- (p = 0.01). Cough, sputum and lung condensation syndrom were more observed in PT+ group (p = 0.01). PT- patients had best nutritional status (p = 0.01). The chest X-ray showed more cavitations in the PT+ group (p = 0.000). While, in the PT- group, extra pulmonary lesions as pleural fluid were more frequent (p = 0.02). The full blood count found an anaemia (Hb=9 g/dl) associated to a neutrophilic h yperleucocytosis and an increased e rythrocyte sedimentation at the first hour in the both groups, without significant differance. The rates of CD4, CD8 lymphocytes and the ratio CD4/CD8 were in the normal range. Negative skin tuberculin test was more found in PT- (p = 0.04). The culture of sputum for PT- patients was positive in 15 patients out of 23 (65.2%).

The risk factors of PT- identified are: Age >45 years, HIV infected patients, no expectoration, no or inefficient cough, no cavitations at the Chest X-ray.