Molecular epidemiology of tuberculosis in the north Hokkaido district of Japan

SETTING: The incidence of tuberculosis in Japan has fallen rapidly in the past 50 years, to 27.9 cases per 100000 population in 2001.OBJECTIVE: To assess the molecular epidemiology of tuberculosis in the north Hokkaido district, Japan.DESIGN: Restriction fragment length polymorphism analysis was consecutively performed on Mycobacterium tuberculosis strains from patients with pulmonary tuberculosis from April 1999 to March 2002.RESULTS: Of 229 patients, strains from 227 (99.1%) were available for analysis. The mean age of the patients analysed was 69.4 years. There was one immigrant patient. Two hundred and seven patients had six or more copies of IS6110. Of these, 16 (7.7%) in eight clusters had identical patterns, 120 (58.0%) belonged to five groups that had similar patterns (Dice coefficient >0.7) and 80 (38.6%) belonged to the 35 groups with the most common patterns (Dice coefficient >0.9).CONCLUSION: These results may reflect the epidemiological characteristics, age and migration of the residents and the incidence of tuberculosis of the area, and also those of Japan: many elderly patients were infected in the past, when the incidence of tuberculosis was very high.