[Factors related to the slowdown in the reduction of the tuberculosis incidence rate in Osaka City--structure of the high incidence rate of tuberculosis in Osaka City analyzed by administrative-ward group, five-year period and age group].

The tuberculosis incidence rate in Osaka City is the highest in Japan. We analyzed the incidence rate in Osaka City in five-year period from 1978 to 1997, namely, 1978-1982 (period I), 1983-1987 (period II), 1988-1992 (period III), and 1993-1997 (period IV). Until the first half of 1980, the tuberculosis incidence rate in Osaka City had been dropping every year, but the rate of decline has been slowed substantially or even stopped since 1983. The incidence rate ratio of Osaka City compared with the national rate was 2.0 to 2.3 from 1970 to 1975, but it has been increasing from 1983 and is now higher than 3. We divided 24 wards of Osaka City into five groups based on selected employment indicators of population 15 years of age and over of 1995 National Census. Group A consists of two wards characterized by extremely high unemployment rate, Group B of four wards by high unemployment rate and high rate of manufacturing workers, Group C of six wards by high rate of non-manufacturing workers (tertiary industry workers), Group D of five wards by high rate of manufacturing workers, and Group E of seven wards by residential areas. The incidence rate of Group A had been declining during periods I and II but started to rise after period III. The rates of Group B and C had been declining from period I to II but the decline slowed down substantially even for every age class in periods III and IV. The incidence rates of Groups D and E have been falling. The incidence rate of the 50-69 year-old age group has been increasing substantially. The proportion of newly registered patients in Group A to all patients of Osaka City increased from 25.2% in period I to 32.7% in period IV. The number of newly registered patients of the 40-69 age class in Group A accounted for 45.1% of that in Osaka City in period IV. The slowdown in the reduction of the tuberculosis incidence rate has occurred not in all, but in only a few wards and it is a typical phenomenon of the middle-aged in those wards. It would be worth investigating whether a substantial decline in the tuberculosis incidence rate in Osaka City cannot be achieved by means of uniform control measures for all wards. Intensified tuberculosis control measures should focus on patients in specific wards and age groups.