SOME OBSERVATIONS ON THE STRAINS OF CORYNEBACTERIUM DIPHTHERIAE ISOLATED RECENTLY IN JAPAN

Abstract
The trends of diphtheria cases and deaths per 100, 000 of population and the case-death rate during the past about 50 years in Japan are presented graphically in Fig. 1. After the termination of the World War II the diphtheria incidence in Japan decreased rapidly to the lowest level recorded in 1952 (9.8 per 100, 000 of population) . The highest figures that the epidemiological statistics in Japan experienced were 127.6 and 118.5 in 1944 and 1945, respectively. Towards the end of the year 1953, however, the first sign of increase in diphtheria cases was observed, and thereafter, the morbidity increased again and reached its peak in 1956 with a morbidity of 20.4 per 100, 000 of population, the figure being two times as much as that in 1952. The age distribution underwent a remarkable change during this epidemic and outbreaks in elementary schools showed a tendency to rise. There have been several reports showing increase of the malignant diphtheria cases. However, no increase in the case-death rate has been observed during the period. Several factors have been considered concerning this epidemic. It was already warned by one of the present authors, basing on the results of Schick test performed in several districts of Tokyo and in its neighborhood in the years 1952-1953, that Schick positive rate was very much high, particularly in young children, and that this fact showed the presence in Japan of a danger of new outbreaks of diphtheria (Kurokawa, 1954) . A survey carried out in 1955 by the Ministry of Health and Welfare for the feature of immunity to diphtheria of about 30, 000 children up to the age of 12 years throughout Japan showed approximately 80% of Schick positive rate in the children at the age of 3-5 years, confirming the results of similar surveys previously performed in a smaller scale. On the other hand, the vaccination rate was not so high as expected. According to statistics, the vaccination rate among babies was 50-60% at most even in urban districts. Hirayama (1957) ascribed the cause of the recent epidemics to the influence of the over all ban against general vaccination enforced in 1949 after a tragic accident resulted from preventive vaccination against diphtheria in Kyoto City in the beginning of November 1948 (See Addendum) . As the factors causing an epidemic, not only those concerning host but also those of pathogenic agent must be considered. McLeod and his collaborators (McLeod, 1943, 1950) offered an opinion that there were three cultural types in Corynebacterium diphtheriae and that these types were found related closely with the clinical severity of diphtheria, the outbreak of diphtheria epidemic and the effectiveness of preventive vaccination and serum therapy. Since their opinion was published, a great deal of literatures on the problem have appeared, but the above opinion has always been accepted. During the years 1954-1956 approximately 200 strains of C. diphtheriae were isolated from patients and healthy carriers by various laboratories in various parts of Tokyo, and Kanagawa, Shizuoka, Ibaraki and Chiba Prefectures, all located in the eastern part of Honshu island. Most of them were forwarded to the National Institute of Health for more detailed bacteriological examinations. The present authors attempted to scrutinize the factors relating to the recent epidemics from the point of view of the pathogenic agent, using these strains. In the present report, some of our examinations performed on several factors thought to be relative to the recent epidemics are to be described.

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