To clarify the characteristics of the tuberculosis situation in Japan, it was analysed in comparison with those in other developed countries. The results are summarized as follows: 1. The tuberculosis epidemic peaked at the end of 1910s in Eastern Japan, and in the 1940s in Western Japan. It is estimated that the annual risk of tuberculosis infection was 4% or more until the end of the World War II. Tuberculosis has spread much later and was much more prevalent up through the 1940s in Japan than in other developed countries. 2. A modern tuberculosis control programme including active case-finding, isolation of infectious cases, charge free medication and BCG vaccination was launched in 1951, and in 1961 an effective case-holding system was established. Tuberculosis incidence decreased rapidly thereafter. As the rate of decrease was almost the same as that of the Inuit (Eskimo) (Fig. 1), one might say that Japan is one of the countries where tuberculosis incidence decreased most rapidly. 3. Incidence of tuberculosis in children is 2.1 per 100,000 in 1991 which is lower than that of the U.S.A. (3.1 per 100,000). 4. Incidence of tuberculosis among the aged is much higher than that of other developed countries as shown in Fig. 3. Of course, this is mainly caused by the fact that a higher percentage of Japanese aged 55 years or more was infected with tubercle bacilli in the past.(ABSTRACT TRUNCATED AT 250 WORDS)
A workshop on the Scientific Issues Relevant to Assessment of Health Effects from Exposure to Methylmercury was held in Raleigh, North Carolina, November 18-20, 1998. At that time, most discussions focused on two of the major epidemiologic studies, e.g., Seychelles child development study and Faroese birth cohort study, associating methylmercury exposure with an array of developmental measures in children. These two studies seemed to provide different conclusions on the potential health effects of methylmercury and significant uncertainties remained because of issues related to exposure, neurobehavioral endpoints, confounders and statistics, and design. Since then, each group researching the Seychellois or Faroes cohort has reported some new findings on the risk assessment of methylmercury. This article is intended to present an overview of the above research, as well as benchmark dose calculations. One implication is that neuropsychological measures may depend on social and cultural factors including race and language, and another is that a key to resolve whether the exposure has harmed the fetus appears to lie in neurophysiological measures such as brainstem auditory evoked potentials and electrocardiographic R-R interval variability. In addition, it is likely that the findings published tend to underestimate the neurotoxic effects of developmental methylmercury exposure. In light of the precautionary principle, a conclusion on health effects of low-level dietary exposures to methylmercury needs to be drawn from all available data including the New Zealand study.
"Streptococcus milleri group" are the part of the indigenous oral flora, and they are proposed to contain three distinct species: Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius. Though not included in the approved lists of bacterial names, "S. milleri group" are regarded as the causative organisms of suppurative infections, such as oral abscess, brain abscess, lung abscess and empyema. I have studied the clinical significance of the "S. milleri group" in respiratory infections. An investigation was performed to confirm the incidence of "S. milleri group" colonization in healthy 120 volunteers' (20 y/o-80 y/o) throats, and it was found that 11.7% (14/120) were positive. On the other hand, attention should be paid to the fact that the "S. milleri group" was highly isolated, 24 (24.7%) in 97 purulent respiratory specimens (94 sputa and 3 throat swabs) from which no other significant microorganism was recovered. I have measured the serum antibody titers of the "S. milleri group", employing the IFA technique, in 10 patients from whose specimens "S. milleri group" was predominantly isolated, and compared with those of 18 healthy volunteers. Whereas all of the titers of healthy volunteers reveal less than 1:256, those of the patients reveal more than 1:512. And antibody titers to "S. milleri group" showed the highest in two weeks after "S. milleri group" isolation, and came down to healthy adult levels in six weeks or more. Thus far, about half of the causative organisms of acute pneumonia have been reported unknown. In this study I have suggested that the "S. milleri group" plays an important role as the causative organism in respiratory infections including pneumonia.
The current BCG vaccination program of Japan is critically discussed based on recent knowledge, especially with regard to its epidemiological aspects, in order to put the problem into perspective for Japan's future tuberculosis control program. 1. EFFICACY AND OVERALL EFFECTIVENESS: Various indicators of BCG efficacy have been proposed, and the meticulous analysis on the variability and the quality of these indicators seems to have formed a consensus on the efficacy, as seen in the recent meta-analysis studies. However, much has been left unanswered concerning the conditions under which the efficacy is guaranteed. The impact of the vaccination program on the population should also be considered in order to make decisions on the program. Comparing the age-specific tuberculosis notification rate between Japan and the USA, where there has been no BCG vaccination program, shows that the rate for 0 to 4 year olds is clearly lower in Japan than in the USA, while it is more than five times higher for all ages in Japan than in the USA. The statistics for Japanese children are superior to those of US children with respect to the speed of decline in notification rate as well. These observations support the overall effectiveness of BCG vaccination in Japan. 2. MECHANISMS OF BCG VACCINATION EFFICACY AND ITS DURATION: Two possible mechanisms of how BCG works to prevent tuberculosis were proposed. Epidemiological models based on each mechanism were subsequently tested by simulating 20 years' development of cases in the BCG vaccination trial by BMRC. In mechanism 1, the BCG-induced immunity is assumed to boost TB immunity in inhibiting the clinical breakdown of tuberculosis during the 10 to 15 years after the vaccination. In mechanism 2, the immunity makes the infection process abort (presumably, at 90%, during the seven years after infection, for example), leading to a smaller risk of future clinical development. So far, most epidemiological models implicitly assume mechanism 1 above. In animal experimental models, however, it has been difficult to simulate the mechanisms differentially, which has been one of the drawbacks to this argument. 3. EFFECTIVENESS OF REVACCINATION: Revaccination with BCG vaccine aims to restore or to endow immunological resistance through repeating vaccination to those who have partially or totally lost the immunity acquired from the primary vaccination. Although some animal experiments support the efficacy of revaccination with BCG, studies in humans have been rare and the results are variable. The observation of Polish infants and schoolchildren is suggestive of the efficacy, but it is not randomized and of questionable value. The recent study of Malawi is a randomized trial. It demonstrated that BCG revaccination protects against leprosy, but does not protect significantly against tuberculosis. It is possible, however, that it does protect against tuberculous lymphadenitis. The two above-mentioned possible mechanisms of BCG immunity were applied to a model analysis of BCG revaccination. It was known that revaccination effectiveness is very limited under any assumption, given the current Japanese epidemiological situation of tuberculosis, so that the demerits due to revaccination, such as strong local reactions, must not be neglected but should be carefully considered. At the same time, we should remember that this model analysis assumes that the primary vaccination is given to new borns with advanced and uniform techniques, which is not always true, and revaccination may supplement the technical failure of the primary vaccination. 4. DECIDING ON THE TOTAL DISCONTINUATION OF BCG VACCINATION PROGRAMME, JAPAN: The recommendations of WHO or IUATLD on the discontinuation of the BCG vaccination program are just conventional ones and the theoretical reasonings is difficult to accept. After all, the decision making should depend on the lay decision makers' subjective judgment balancing benefit and loss in terms of costs and health incurred by the policy, as shown by Waaler and Rouillon. The current Japanese BCG vaccination program is very expensive, but brings about some, though very small, benefit. This balance was compared with that of Sweden around 1975, when the program was discontinued. The comparison clearly showed that the cost-effectiveness of the program in Japan today in superior to that of Sweden in 1975.