[Molecular epidemiology of tuberculosis by the use of IS6110 restriction fragment length polymorphism: a study from 2001 to 2003].

OBJECTIVE To analyze the situation of tuberculosis infection by DNA fingerprinting in the middle and eastern part of Osaka, Japan. DESIGN We performed IS6110 restriction fragment length polymorphism (RFLP) on 1200 isolates from tuberculosis patients who visited our hospital from January 2001 to December 2003. A cluster was defined as a series of isolates with more than 90% similarity by IS6110 RFLP and those with the same drug-susceptibility pattern. The isolates with fewer than six copies of IS6110 were considered to be clustered if the IS6110 RFLP patterns and the variable numbers of tandem repeats with 16 regions of ETR and MIRU "allele profile" were identical. RESULTS The number of samples in incremental study periods was 422 in 2001, 817 between 2001 and 2002 and 1200 between 2001 and 2003. The percentage of clustered cases was 27.8% in 2001, 19.1% in 2002 and 19.5% in 2003. The cumulative percentage of clustered cases was 27.8% in the first year, 29.7% over two years and 32.6% over three years. The percentage of clustered cases of isolates with a drug resistance was significantly lower (25.0%) than that of drug susceptible isolates (33.7%). Next, we investigated the clustered cases by gender and age. The percentage of clustered cases with isolates from young males and females (0-19 years old) was 23.8%. In contrast, the percentage of clustered cases with isolates from 20-59 year-old females gradually decreased from 14.7% to 4.4%. Conversely, the percentage of clustered cases from young and middle aged male (20-59 years old) was higher (20.2%-32.4%) than that of females. CONCLUSION The sharp increase in the cumulative cluster formation rate was curbed by the decline in the tuberculosis incidence rate in Osaka, Japan, after the first year of examination. We thought that this phenomenon suggests the success of the anti-tuberculosis measure in Japan.