Epidemiological Studies on Subacute Myelo-optico Neuropathy (SMON) in the town of Yubara, Japan (Report 2)

SMON (subacute myelo-optico neuropathy) which broke out in Yubara, Japan was studied by examination of public records kept by the Town authority, responses to questionnaires by all the families in the town, interviews with patients and home visits in order to investigate environmental conditions.Some of the results have been published previously in this journal. This will be the second publication in this series, chiefly based on the second field survey performed at the beginning of this year. The results are as follows:1) In Yubara township, located in the northern part of Okayama Prefecture, an outbreak of SMON was reported at the beginning of 1967. The incidence increased gradually, reaching its peak in September 1968, and then diminished slowly during 1969. There were no cases of SMON reported in 1970. (until March) Total number of the cases reported were 81. The yearly incidence rate is 486per 100, 000 population during the 3 year period.2) Sex ratio was 3.3 females to 1 male patient. As for age distribution, males revealed highest rate in their thirties, while females showed high rates in those aged from twenties to sixties. The phenomenon called “die Prazession der Durchseuchung, ” was not observed.3) Geographical distribution spread from the center to the peripheral parts of the town each year.4) Although cluster of cases were found within families and their social contacts, no one could be identified as the source of spread.5) Caterers, sales men and women, local public health employees and hospital employees were noted to have high attack rates in the early stages of the epidemic, but the disease later spread among farmer population as well.6) Appendicitis, appendectomy, chronic diseases and constitutional disorders were more frequently observed in the medical histories of the patients than in the control group.7) The results of water examination by the local health center, showed occasional coli-contamination of the local water supply during the summer months.