The Topic of This Month Vol.17 No.3 (No.193)

The trend of aseptic meningitis and the viruses implicated, 1995

Aseptic meningitis is caused mainly by such enteroviruses as echoviruses (E) and group B coxsackieviruses (CB) and mumps virus. In Japan, patients of aseptic meningitis due to enteroviruses increase in number mostly in summer every year (Fig. 1).

Aseptic meningitis patients reported for 1995 in the National Epidemiological Surveillance of Infectious Diseases (NESID) numbered 1,619 (3.10 patients per sentinel hospital), being the fewest ever reported. The patients at ages of 0-4 years accounted for 44%, 5-9 years 38%, 10-14 years 9.5%, and greater equal 15 years 8.5%. The proportion of 0-year-olds (18%) was the highest after the start of NESID in 1982 (Fig. 2).

In 1995, virus isolation from 440 meningitis patients was reported to IASR (as of February 20, 1996). Of these isolates, 113 (26%) were CB5, 75 (17%) E7 and 69 (16%) CB3. Isolation from cerebrospinal fluid was in 92, 58, and 46 patients, respectively (Table 1). Reports on isolation of E9 were plenty during 1990 through 1994 but markedly decreased (311 in 1994 versus nine in 1995) (see IASR Vol. 16, No. 3).

Reports on monthly isolation of CB5, E7, and CB3, of which isolation from meningitis patients was frequent in 1995, are depicted for 1994 and 1995 in Fig. 3. Isolation of both CB3 and CB5 was reported every month in 1995 as was the case in 1994 (see IASR Vol. 16, No. 8), with the largest number of reports in July. In 1995, 375 reports on isolation of CB3 were provided by 37 laboratories and 219 of CB5 by 25 laboratories (108 were from Kagawa prefectural PHI) in the whole country. Isolation of E7 has been reported every month since April 1995 and the number of reports has been increasing even after the summer. There were 217 reports of isolation from 22 laboratories in Tottori (see p. 49 of this issue), Fukushima, Shimane and other prefectures.

Isolation of E7 has continually been reported even after the epidemic season for enteroviruses. According to the previous reports of isolation of E7 by the participating laboratories (Table 2), there was a large-scale epidemic in 1986 (see IASR, Vol. 8, No. 1) and the viruses were isolated frequently in Aichi, Gifu and some other prefectures. Reports on virus isolation were few in 1987-1992 in the whole country. There were local epidemics in 1993 (see IASR, Vol. 14, No. 8), but the reports on virus isolation were few in 1994.

The age distributions of patients including those diagnosed as meningitis, from which CB5, E7 or CB3 was isolated, are shown in Fig. 4. Of the patients from which CB3 or CB5 was isolated, 0-year-old ones were the largest in number. Meningitis was frequently reported with such 0-year-old patients, infrequently with 1 to 2-year-old ones, and also frequently with over 3-year-old ones (see IASR, Vol. 16, No. 8). Of E7-isolated patients, like CB-isolated ones, meningitis was frequently reported with 0-year-old patients but infrequently with 1 to 2-year-old ones. The 0-year-old meningitis patients were looked more in detail into ages in months; the proportions of 0 to 2-month-old ones accounted for 85% (11/13) in E7-isolated ones, 88% (29/33) in CB3-isolated ones, and 66% (21/32) in CB5-isolated ones. The proportion of over 3-month-old ones was low.

The reports on virus isolation from last autumn to winter are only provisional and more reports will be added from now on. The trend of E7, the reports on whose isolation have been increasing since last summer, deserves attention.

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