Increasing drug resistance of Mycobacterium tuberculosis isolates in a medical center in northern Taiwan.

BACKGROUND/PURPOSE This retrospective study was conducted to evaluate the drug resistance patterns of Mycobacterium tuberculosis in a medical center in northern Taiwan between 2003 and 2004 in comparison to those reported in 1990-1992. METHODS A total of 611 non-duplicate M. tuberculosis isolates from culture-proven tuberculosis (TB) cases were tested for drug susceptibility against five first-line anti-TB drugs in a clinical mycobacterial laboratory using the agar proportional method for isoniazid (INH), rifampicin (RIF), ethambutol (EMB), and streptomycin (SM). The Wayne assay, which measures the activity of pyrazinamide (PZA), was used for PZA susceptibility testing. RESULTS Of 611 patients, including 510 males and 101 females, 70.2% of patients were older than 65 years. A total of 339 isolates (55.5%) were resistant to one or more drugs. Isolates from patients aged <25 years showed a significantly higher drug resistance rate (79.2%) compared with other age groups (p=0.0312). Single-drug resistance was observed in 97 (15.9%) of all isolates. Monoresistance to PZA (8.0%) was most frequent, followed by INH (5.1%), RIF (0.5%), EMB (1.6%), and SM (0.7%). Among the polydrug resistant isolates (PDR-TB), resistance rates were 35.5% for INH and 27.0% for RIF. One hundred and fifty-nine isolates (26.0%) were resistant to both INH and RIF (multidrug-resistant [MDR] TB); 94.6% of RIF-resistant isolates were also resistant to INH. The overall drug resistance rates and percentages of PDR-TB and MDR-TB increased over the 12-year study period (p<0.001). Based on medical records, primary cases were identified in 486 (84.7%) out of 574 patients, and resistance to any drug was identified in 268 (55.1%) patients, of which 130 (26.7%) were MDR-TB. Among the 88 with recurrent TB, 54 (61.4%) were resistant to at least one drug, and MDR-TB was identified in 29 (33.0%) patients. A history of previous anti-TB therapy was a significant factor for overall drug resistance, PZA monoresistance, PDR-TB, and MDR-TB (p<0.001). CONCLUSION The emergence of M. tuberculosis isolates resistant to anti-TB agents in this hospital, and in particular among young patients, is alarming. Strict measures to control and prevent drug-resistant TB are urgently needed.