Restriction fragment length polymorphism study of nationwide samples of Mycobacterium tuberculosis in Thailand, 1997-1998

SETTING: During 1997-1998, a national anti-tuberculosis drug resistance survey was conducted in Thailand as a part of a global project.OBJECTIVE: To evaluate the IS6110 hybridisation patterns and the level of clustering, which was expected to be low due to the short duration of the sample collection.DESIGN: Eight hundred and twenty-eight bacterial isolates were available for fingerprinting by standard IS6110 hybridisation.RESULTS: The restriction fragment length polymorphism patterns varied with geographic locations, ages of the patients, and resistance to rifampicin and streptomycin. The Beijing strain was more common among younger patients, and their prevalence appeared to decrease with the distance from Bangkok, while the opposite was true for the single-banded isolates. Excluding isolates containing five or less copies of IS6110, 26.4% were clustered. Clustering was more common among females. The clustered isolates were sometimes from different provinces and, if resistant to drugs, usually possessed different resistance profiles.CONCLUSIONS: The results question the validity of inferring recent transmission from the clustering of IS6110 hybridisation patterns in some settings in Thailand. The level of recent transmission in a nationwide study in a country with a high incidence of tuberculosis should be evaluated with caution.