The Topic of This Month Vol.17 No.2 (No.192)
In the National Epidemiological Surveillance of Infectious Agents (NESID), incidence of gastroenteritis patients is reported in two categories, "infectious gastroenteritis" and "infantile vomiting and diarrhea", distinguished by sentinel clinics of pediatricians/general physicians. Since 1987, cases of gastroenteritis of 0 to 3 years of age, clinically suspected of rotavirus infection, have been reported as "infantile vomiting and diarrhea" and other cases of gastroenteritis as "infectious gastroenteritis". Cases of these two diseases have tended to increase markedly in winter every year (Fig. 1). In winter, reports on detection of such gastroenteritis viruses as rotavirus and small round structured viruses (SRSV) also have tended to increase (see IASR, Vol. 10, No. 4; Vol. 12, No. 5; Vol. 14, No. 3; and Vol. 16, No. 2). This topic deals with the analyses made on the reports of cases of these two diseases, being regarded as a single clinical entity, gastroenteritis.
In the 1995/96 season, reports of gastroenteritis patients to NESID increased earlier than in the preceding years (Fig. 2), and by the 48th week reached the largest number ever reported since 1981 when collecting the information was started. The reports of patients in October- December 1995 (the fourth quarter) outnumbered largely those during the same period in the previous years.
The trend of incidence of gastroenteritis patients in the fourth quarter of 1995 by prefecture is shown in Fig. 3. The number of patients per sentinel clinic exceeded eight in the 43rd week in Saitama and Oita Prefectures and in the 44th week in Tokyo Metropolitan and Kyoto Prefecture. Subsequently, the epidemics have spread to wider areas, excepting Hokkaido and Okinawa Prefectures. The peak of incidence by district was seen in the 46th week in the Kanto/Koshin-etsu district, in the 48th week in the Tokai/Hokuriku and Kinki districts, in the 49th week in the Chugoku/Shikoku and Tohoku districts, and in the 50th week in the Kyushu/Okinawa district. The age group of 0-4 years accounted for 63% of all the patients (Fig. 4).
Update for virus detection: In the past gastro-enteritis epidemics, reports on detection of rotavirus furnished to IASR increased in response to the increase in number of cases, but it is noticeable that in the epidemic in the fourth quarter of 1995, detection of rotavirus was seldom reported (Table 1). It is expected that more reports on virus detection will be added from now on, but rotavirus was detected only in two instances in October and in one instance in November as of January 22, 1996.
On the contrary, during October through December 1995, SRSV were detected by electron microscopy (EM) from sporadic cases involving 27 children (three 0-year, 11 one-year, two 2-year, nine 3-year, one 6-year, and one 7-year cases) and two adults (28- and 31-year cases) in Saitama and Osaka Prefectures and Hiroshima and Fukuoka Cities (see p. 44 of this issue). It seems that the epidemics in this season were due to SRSV. It is known that SRSV cause food-poisoning-like outbreaks, but there has been no report on high incidence of SRSV gastroenteritis in wide areas.
In addition, SRSV were detected from children of sporadic cases in this season by EM or reverse transcription-polymerase chain reaction (RT-PCR) in Chiba Prefecture (see IASR, Vol. 17, No. 1), Tokyo Metropolitan (see p. 23 of this issue) and Kanagawa Prefecture (see p. 24 of this issue) (no rotavirus was detected). It was reported that the clinical symptoms of the patients were mainly but few projectile vomitings, which preceded diarrhea. From cases in Tokyo, SRSV were detected by RT-PCR not only from stools but also from vomits.
When none of diarrheagenic bacteria, rotavirus and adenovirus is detected from gastroenteritis patients, it seems justified to look for SRSV and astrovirus. At present, however, no simple method for detection to take the place of EM has been established as yet.