Sputum bacterial load predicts multidrug-resistant tuberculosis in retreatment patients: a case-control study.

BACKGROUND Rapid and effective diagnosis of multidrug-resistant tuberculosis (MDR-TB) is an essential component of global tuberculosis (TB) control, but most MDR-TB cases are still not diagnosed. OBJECTIVE To assess whether patient sputum bacterial load can be used to identify patients at increased risk of MDR-TB. METHODS We used a case-control study and multivariable logistic regression models to investigate associations between MDR-TB and sputum bacterial load, as measured by semi-quantitative microscopy and automated time to detection (TTD) of liquid culture. We assessed data from retreatment TB patients with MDR-TB (cases) and from those without MDR-TB (controls) at a reference laboratory in Cameroon. RESULTS MDR-TB was associated with a smear microscopy grade of 3+ (OR 21.9, 95%CI 6.2-76.8) or 2+ (OR 10.8, 95%CI 2.9-40.7), compared to a result of 1+, scanty or smear-negative among 80 MDR-TB cases and 521 controls. MDR-TB was associated with automated TTD of ⩿160 h (OR 2.2, 95%CI 1.1-4.7) compared to >160 h among a subpopulation of 47 cases and 350 controls. CONCLUSIONS A higher sputum bacterial load is associated with MDR-TB in retreatment patients in Cameroon.