[Tuberculosis prevalence survey in Japan].

Chest X-ray examination had been used rather soon after the discovery of X-ray by Rontgen K in 1895 as it was possible to detect chest abnormality by simple radiography. After the discovery of radiophotography independently by Abreu M and Koga Y in 1936, it was applied as a method of mass screening for TB in Japan, and Imamura A made a special lecture on "The mass screening for TB" using radiophotography in 1940 in the Annual Meeting of the Japanese Society for TB. From experiences of mass screening, it was found that there were many cases of TB who do not aware of their own disease, and to know the prevalence of TB, the screening of survey subjects by X-ray examination is indispensable. Noticing the importance of mass health examination by chest X-ray, Dr. Tanaka S, then director of information division, JATAHQ, edited a book entitled "How to carry out mass health examination for TB" in 1951, then he moved to the Ministry of Health and Welfare and engaged in the preparation of the first TB prevalence survey. Random sampling technique was already developed, and health center network covering the whole country was already completed in early 1950s. Using these background, the first TB prevalence survey was conducted in 1953. TB Prevalence Survey Committee was organized asking cooperation of experts in TB, epidemiology and statistics, and the survey in sampled area was carried out by a survey team headed by the director of health center in charge of the sampled area. The survey teams engaged in the survey with enthusiasm, and the rate of response to the survey was 99.3%. The result of this survey was published in the WHO Bulletin, 1955. After the survey in 1953, the following prevalence surveys were carried out in 1958, 1963, 1968 and 1973. Outline of these surveys was shown in Table 1, and the rate of examination was high in all, except the survey in 1973. In this year, TB prevalence survey was carried out in conjunction with the national nutritional survey and the national mental health survey, and unfortunately, there were some opponent groups against the national mental health survey, which affected the rate of response to the TB survey, too. In addition to the 5 prevalence surveys, one thirds of the survey population in 1953, 1958 and 1963 was surveyed in the next year to know the incidence of TB. Follow-up survey on active TB cases found in the 1953 and 1958 survey was carried out in 1964, and similar follow-up survey was carried out in 1968 for active TB cases found in 1953, 1958 and 1963 surveys. Moreover, survey subjects excluding active TB cases in 1968 were followed up until 1973, and the incidence of newly registered TB cases during this period was surveyed. Summarized results of TB prevalence surveys are reported. The first survey was carried out in 1953, and had been repeated every 5 years until 1973. As national TB control program (NTP) under new TB Control Law had been implemented since 1951, the results of 5 surveys clearly indicated the outcome of NTP of Japan. Age-specific prevalence of active TB in 5 surveys is shown in Fig. 1. Due to advances in chemotherapy, there was certain difference in the definition of active TB in 1953 and 1958, and chemotherapy was indicated more widely for those with TB pathology in lung in 1958. Comparing the age-specific prevalence of active TB in 1953 and 1958, the prevalence decreased in 1958 below 35 years of age, and increased above 35 years. The decline in the prevalence of active TB in age groups below 35 in spite of widening of definition of active TB in 1958 indicated the efficacy of TB control with mass screening and BCG vaccination and treatment for detected cases. As the definition of active TB had been unchanged since 1958 up to 1973, the decline in the prevalence of active TB seen in all age groups clearly indicated the achievements of NTP. Overall trend of prevalence of active TB, cavitary TB, bacillary TB and smear+PTB in 5 surveys is shown in Fig. 2 together with epidemiological figures obtained from vital registration, namely incidence of TB, prevalence of active TB at the end of the year and TB mortality. In analyzing the results, we have to take note of the difference in bacteriological examination methods. As laryngeal swab method was used in 1963 and 1968, culture positive rate was lower and no information about smear examination, however, from 1958 to 1973, all indices had declined exponentially with similar speed including prevalence of smear +PTB and bacillary TB if results in 1958 and 1973 were connected directly. Based on this results and the fact that marked decline in the prevalence of active TB requiring much larger sample size for the survey, TB prevalence survey was stopped, and data from vital register has been used since then to evaluate the TB situation. Results of 3 incidence surveys were shown in Fig. 3. Shift of higher incidence from younger age groups to higher age groups was clearly shown from 1954 survey to 1964 survey. The results of routine follow-up by vital registration of 1968 survey population excluding TB cases found in 1968 survey were shown in Table 2, and high risk groups were clearly shown in this table. As routine X-ray examination was done by radiography in 1963 survey, it was possible to pick up any slight TB pathology, and the age-specific prevalence of any TB finding, that of healed findings and of calcified lesions were shown together with BCG vaccination coverage in Fig. 4. In the age groups above 40, the prevalence of any TB finding, as well as of healed and calcified findings was very high, while the coverage of BCG vaccination was below 20%. BCG vaccination was started in Japan in 1943, and those above 40 years of age in 1963 were then already 20 years of age or above, and only few were vaccinated with BCG when BCG vaccination was expanded to cover higher age groups thereafter. TB prevalence survey has now come to be used as one of methods to estimate the incidence of TB under the impact of HIV/AIDS epidemic, and its significance is now re-evaluated.