Epidemiological studies on subacute myelo-optico-neuropathy with abdominal symptoms (SMON) in epidemic area of Okayama Prefecture, Japan. XI. Epidemiological studies on SMON

Epidemiological study on the prevalence of SMON III Ibara City, Yoshii Town and Yubara Town in Okayama Prefecture was conducted and the following results were obtained. "Epidemization precession" (Die Prazession der Durchseuchung), described by Rudder which shows that ages common to this disease is shifting to younger generation as incidence rate increases, in the endemic regions was recognized in Ibara City and Yubara Town. The mode of the distribution of the interval between the primary and secondary patients in a family suggests that it corresponds to the incubation period. Distribution of the patients to the size of family is not adaptable to binomial model, but adaptable to chain binomial model, and the intra-household transmitted rate is 5 per cent, and the true intra-household transmitted rate is about two times as high as extra-household transmitted rate by the modified chain binomial model. Intra-hospital incidence among SMON patients and non-SMON patients as well as medical workers were observed at the time when the number of new patients increased in a hospital. In SMON patients, the rate of appendectomized ones was higher than that of non-SMON patients, suggesting that gastrointestinal tract has some relationship to the development of SMON disease.