Factors associated with primary rifampicin-resistant/multidrug-resistant TB: a case-control study

BACKGROUND Multidrug-resistant TB (MDR-TB) threatens TB control in Bhutan. According to the 2017 national Drug Resistance Surveillance report of the Royal Centre for Disease Control, 13.7% of new pulmonary TB cases had rifampicin resistance, of whom 98% were also resistant to isoniazid. We investigated the factors associated with primary rifampicin-resistant/multidrug-resistant TB (RR/MDR-TB) among new pulmonary TB patients. METHODS We conducted a nationwide case-control study including 46 laboratory-confirmed primary RR/MDR-TB cases and 138 drug-susceptible pulmonary TB controls (1:3 ratio). Multivariable logistic regression identified factors independently associated with primary RR/MDR-TB. RESULTS Factors associated with primary RR/MDR-TB were delay in diagnosis (adjusted odds ratio [AOR] 24.9, P < 0.001), poor household ventilation (AOR 3.6, P = 0.023), contact with MDR-TB patients (AOR 7.2, P < 0.001), living alone (AOR 10.8, P = 0.016), perceived health staff unfriendliness (AOR 9.6, P = 0.004), and TB medicine unavailability (AOR 16.5, P = 0.024). Increasing age was associated with lower odds of RR/MDR-TB (AOR 0.94 per year, P = 0.005). CONCLUSION Primary RR/MDR-TB in Bhutan was strongly associated with delayed diagnosis, contact with known MDR-TB patients and modifiable health-system factors. Expanding rapid molecular testing, strengthening contact investigation, and improving patient-centred care are critical to interrupt transmission and sustain TB control gains.