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Epidemiological Studies on Echovirus Type 18 Infection in Toyama Prefecture

Echovirus type 18 (echo 18) was isolated from six aseptic meningitis children in Fukumitsu‐machi, Toyama Prefecture, from July to August, 1980. This was the first virologically‐confirmed epidemic of aseptic meningitis due to echo 18 in Japan. Epidemiological studies on the prevalence of this virus among the inhabitants in Toyama Prefecture were also performed. The results are summarized as follows. (1) Significant increases in neutralizing antibody titers against echo 18 were observed in all the paired sera of aseptic meningitis patients from whom echo 18 was isolated. (2) In October, 1980, echo 18 was also isolated from healthy children or from infants suffering from gastroenteritis in other areas of Toyama Prefecture. (3) Among the sera collected from 50 children (aged ≤ 12) in Fukumitsumachi in December, 1980, neutralizing antibodies against echo 18 were detected only in the younger groups (aged ≤8), 58.9% of these age groups showing a titer of 4 or higher. (4) Another epidemic around 1963 by echo 18 in Toyama Prefecture was retrospectively suggested by the examinations of sera collected in 1978 and 1981 from inhabitants in various areas of Toyama Prefecture. (5) Neutralizing antibody titers against the strain isolated, No. 35′80, were significantly higher than those against strain ‘Metcalf,’ the prototype of echo 18, in most sera including both aseptic meningitis patients and healthy inhabitants.