The Topic of This Month Vol.19 No.11(No.225)
Under the National Epidemiological Surveillance of Infectious Diseases (NESID) program, about 2,500 sentinel clinics of pediatricians/general physicians throughout Japan report gastroenteritis affecting infants of 0-3 years old, that is suspected of rotavirus infection on the basis of clinical diagnosis, as "infantile vomiting and diarrhea". At prefectural and municipal public health institutes (PHIs), detection of viral pathogens from stool specimens of gastroenteritis patients (including infantile vomiting and diarrheal cases) collected at some of the sentinel clinics is being undertaken. The data obtained by the infectious agents surveillance have been compiled in the Infectious Agents Surveillance Report (IASR). From these data, rotavirus and small round structured virus (SRSV) have been identified as the main viral pathogens that cause gastroenteritis epidemics among Japanese infants and children, and the epidemic patterns of these virus infections have been clarified recently.
The trend of the reports on "infantile vomiting and diarrhea" cases per sentinel clinic during the 1987/88-1997/98 seasons (illustrated in Fig. 1) shows a marked increase in the winter season of each year. However, a considerable number of cases have been found in spring, particularly in the 1997/98 season. A temporary decrease in cases was seen during the 6-8th weeks of 1998 (in late February), a second epidemic was clearly seen with the largest number of cases in the 14th week (early April).
Reports of rotavirus, SRSV, astrovirus, and adenovirus types 40/41, known as viral agents of gastroenteritis, are illustrated for five seasons during October 1993-September 1998 (Table 1). Due to the difficulty in culturing these gastroenteritis viruses, etiological diagnosis greatly depends on direct detection by electron microscopy and antigen detection by enzyme immunoassay (EIA), reversed passive hemagglutination (RPHA), and latex agglutination. Approximately 400-700 reports on detection of group A rotavirus have been made every season. Although there have been only a small number of reports on detection of group C rotavirus, a few outbreaks have occurred in elementary schools (see p. 252 of this issue and IASR Vol. 18, No. 12). No report on detection of group B rotavirus has been made. There have been over 200-300 reports per year of SRSV detected mainly by electron microscopy. There have been few reports of astrovirus in recent years, although a large outbreak of astrovirus diarrhea in elementary schools in Osaka was reported in 1991 (see IASR Vol. 13, No. 4). Since antigen-detection kits have come into wider use, the number of reports of adenovirus types 40/41 have increased gradually, numbering 77 in the 1997/98 season.
The weekly detection of rota-virus, SRSV, and adenovirus types 40/41 during the period from October 1993 to September 1998 is illustrated in Fig. 2. The virus-detected cases were categorized into three groups by age: 0-3 years, 4-14 years, and 15 years and older. Before the 1993/94 season, reports of rotavirus increased in correlation with peak occurrence of "infantile vomiting and diarrhea" (see IASR, Vol. 12, No. 5; Vol. 14, No. 3; Vol. 16, No. 2). During the 1994/95 season, reports of rotavirus were relatively few when compared to the increased number of patients at the end of 1994. Although the number of patients increased earlier than usual in the first half of the 1995/96 season (the fourth quarter of 1995), there were very few reports of rotavirus in contrast to more frequent detection of SRSV. This may indicate that SRSV was the principal viral agent of "infantile vomiting and diarrhea" at that time (see IASR Vol. 17, No. 2). In the latter half of the 1995/96 season (the first half of 1996), detection of rotavirus from infants aged 0-3 years increased. The same trend was also noted in the 1996/97 and 1997/98 seasons: SRSV was detected in infants with gastroenteritis in winter and rotavirus in spring. In the 1997/98 season, occurrence of "infantile vomiting and diarrhea" formed a bimodal trend (Fig. 1): the first peak was attributed to SRSV and the second one to rotavirus.
The age distribution of children (0-14 years), from which rotavirus, SRSV, or adenovirus types 40/41 was detected in the 1997/98 season (from October 1997 to September 1998) appears in Fig. 3. Detection of rotavirus or SRSV was most frequent in children of one year old, while that of adenovirus types 40/41 in 0-year old infants. The 0- to 3-year old children accounted for 87%, 66%, and 85% of rotavirus-, SRSV-, and adenovirus types 40/41-detected cases, respectively. The ratio of SRSV detection from children over the age of four, particularly elder children, was higher than that of rotavirus or adenovirus types 40/41 detection.
The clinical symptoms of children from which rotavirus, SRSV, or adenovirus types 40/41 was detected in the 1997/1998 season were compared (Table 2). Fever was recorded frequently in both 0-3 years and 4-14 years old groups of rotavirus-detected cases. Gastrointestinal symptoms were looked at in detail; those having nausea/vomiting only accounted for 14% of SRSV-detected children aged 4-14 years. The ratio was higher than that in children aged 0-3 years (6.5%).
It is known that outbreaks of SRSV gastroenteritis have occurred among adults from consuming such foodstuffs as raw oysters (see IASR, Vol. 19, No. 1). Most of the SRSV-detected patients at age over 15 years (Fig. 2) were those implicated in such outbreaks. SRSV causes outbreaks of adult gastroenteritis and infantile gastroenteritis epidemics as described above.
In August 1998, the US Food and Drug Administration approved the use of a rotavirus live oral vaccine [tetravalent rhesus-human reassortant rotavirus vaccine (RRV-TV)] within USA for its expected cost-effectiveness in reducing diarrheal diseases of children (CDC, EID, Vol. 4, No. 4, 1998). Clinico-epidemiological investigations on demanding for rotavirus vaccines have been carried out also in Japan.