Objective: To study changing trends in TB epidemiology with emphasis on drug resistance rates in various age groups from 1986-1999.
Design: Laboratory-based data on drug susceptibility testing against streptomycin (SM), isoniazid (NH), rifampicin (RMP) and ethambutol (EMB) had been collected continuously in a centralised TB laboratory in Hong Kong. Epidemiological parameters such as sex, age and drug resistance rates in new and retreatment cases were measured and analysed for longitudinal trends.
Results: Of 48 924 non-duplicate isolates from new TB cases, 7045 (14.4%) were resistant to one or more drugs, 5773 (11.8%) were resistant to SM and/or INH while 881 (1.8%) were multidrug-resistant (MDR-TB). Of 3857 isolates from retreatment patients, 1176 (30.5%) were resistant to one or more drugs, 616 (16.0%) were resistant to SM and/or [NH, and 467 (12.1%) were MDR-TB. For isolates from new cases, significant declines were observed in the resistance rates against any drug, SM alone, INH alone, SM+INH and INH+RMP. For retreatment isolates, significant declines were also observed in resistance to any drug and INH+RMP. In both new and retreatment cases, isolates from patients aged over 65 years showed significantly lower drug resistance (any drug and INH+RMP) compared with other age groups (16-34 years and 35-65 years).
Conclusion: With successful implementation of DOTS over a 14-year period, laboratory-based surveillance data showed significant declines in drug resistance, including MDR-TB. This has occurred amidst demographic changes associated with a generally ageing population as well as highly mobile sectors that are in constant exchange with highly endemic areas.