Nature of drug resistance and predictors of multidrug-resistant tuberculosis among patients seen at the Philippine General Hospital, Manila, Philippines.

SETTING: This study was conducted at the University of the Philippines--Philippine General Hospital (UP-PGH), Manila, Philippines.
OBJECTIVES: To determine the nature of drug resistance among patients with pulmonary tuberculosis (PTB), and to establish clinical predictors of drug-resistant tuberculosis.
DESIGN: Descriptive, prospective study.
METHODS: Patients with positive culture for Mycobacterium tuberculosis were interviewed regarding past history of anti-tuberculosis treatment, BCG vaccination, chest X-ray and family contact. M. tuberculosis isolates from 299 patients were tested for susceptibility to rifampicin, isoniazid (INH), ethambutol and streptomycin using the submerged disc proportion method. Pyrazinamide (PZA) susceptibility test was done with standard laboratory powder in 7H10 media.
RESULTS: Of the 299 M. tuberculosis isolates, 17% were fully susceptible to the 5 primary drugs and 54% were resistant to 2 or more drugs (multidrug resistant TB [MDR-TB]). Initial drug resistance rate was high with ethambutol (39%) and INH (17%). Previous history of anti-tuberculosis treatment was significantly associated with MDR-TB (Odds Ratio [OR] 2.44, 95% confidence interval). Incomplete anti-TB treatment taken for longer than 3 months increased the likelihood of MDR-TB (OR 4.6, P < 0.0001).
CONCLUSION: The high rate of MDR-TB was associated with previous anti-tuberculosis treatment. The chance of developing MDR-TB was significantly increased when inadequate prior treatment was given for more than 3 months.