Through the National Epidemiological Surveillance of Infectious Diseases (NESID) based on the Infectious Diseases Control Law (enacted in April 1999 and amended in November 2003), cases of infectious gastroenteritis, a Category V disease, have been reported by approximately 3,000 pediatric sentinel clinics nationwide. Infectious gastroenteritis denotes a syndrome caused by multiple infectious agents, and at prefectural and municipal public health institutes (PHIs), pathogen testing is conducted on fecal specimens of gastroenteritis cases collected by a portion of pediatric sentinel clinics, as part of the Infectious Agents Surveillance. Furthermore, infectious agent testing is also performed at PHIs during outbreaks.
Trends in infectious gastroenteritis under the NESID: Reported cases tend to increase abruptly from November through December every year, decrease between the end of the year and the beginning of the following year, then after another increase, decrease again after March-April (see http://idsc.nih.go.jp/idwr/kanja/weeklygraph/04gastro.html). In recent years, noroviruses have been detected mainly during the first half and rotaviruses during the latter half of epidemics (see IASR, Vol. 19, No. 11 and http://idsc.nih.go.jp/iasr/prompt/graph/sr5.gif). In looking at the infectious agents detected from sporadic cases of infectious gastroenteritis during 2000-2004 by age, a large proportion of rotavirus detections occurred among the younger ages (Fig. 1).
Reports of rotavirus detection: Reports of rotavirus detection peaked during the 1985/86 season, then subsequently decreasing to between 500-800 annual reports in recent years (Table 1). Group C virus has been reported in small numbers with the majority of cases caused by group A virus. During 2000-2004, group A and group C viruses were reported from 53 and 15 PHIs, respectively. Group B virus has yet to be reported in Japan.
Monthly detection of rotavirus (Fig. 2 on p. 3): In any of the seasons during 1979/80-1983/84, virus detection peaked in January, while during 1984/85-1988/89, detections peaked in February. Thereafter, detection peaks have tended to occur later; during 1996/97-1997/98, the peak occurred in April. During 1999/2000-2003/04, the peak has occurred in March every year.
Ages of rotavirus-detected cases (Fig. 3): Of the 2,897 cases from which group A rotavirus was detected during 2000-2004, 36% were one year of age, 24% were 0 years, 15% were 2 years, and a few were over 2 years. Of infants 0 years of age, a large proportion were 6 months and older. In contrast, among the 70 cases from which group C virus was detected, 36% were 5-9 years of age and 33% were 10-14 years.
Methods of rotavirus detection (Fig. 4): In 1997, changes were made to the categories of detection methods on the IASR report form. During 1988-1996, the primary methods utilized were enzyme immunoassay (EIA), electron microscopy (EM), and reverse passive hemagglutination (RPHA); latex agglutination (LA) was also used. Since 1997, EIA has become the primary method of diagnosis, although polymerase chain reaction (PCR) and immunochromatography (IC) have been used increasingly since 2000. Because commercial kits commonly used at PHIs can only detect group A virus, reports of group C virus have been scarce. Group A virus has been detected in cerebrospinal fluid of five cases, including a fatal case of encephalitis, by PCR (see p. 13 of this issue).
Outbreak incidents: Although rotavirus gastroenteritis occurs mainly in infants 0-1 year of age, outbreaks have been observed among children in nursery schools, kindergartens and primary schools (see p. 10 of this issue), as well as among adults in hospitals, nursing homes, and other welfare facilities. During 2000-2004, 27 outbreaks caused by group A virus and eight due to group C virus were reported (Table 2). Of the outbreaks involving 50 or more cases, six were due to group A virus and five due to group C virus (Table 3). Person-to-person infection was thought to be the mode of transmission in many of these outbreaks.
G serotyping of group A rotavirus: Group A rotaviruses are comprised of G serotypes 1-14, based on the outer capsid structural viral protein 7 (VP7). P genotyping of the VP4 gene is also conducted. Since January 2004, reports based on G serotyping of group A virus have become possible in IASR. Five PHIs have reported 256 cases retrospectively to 2000, among which G3 was most predominant, followed by G1. EIA and PCR have been utilized equally for most G serotypes, although only PCR has been utilized for G9 and G12 (Table 4).
During 1984-2003, according to laboratory results of pediatric outpatients in five districts (see p. 7 of this issue), the rotavirus-positive rate was approximately 30%; G1-positive rates increased from the latter half of the 1980s to 80-90% of all rotavirus cases in the 1990s, subsequently followed by a sudden decrease. G2-positive rates were 30-40% of rotavirus cases during 2000-2002. Both G3- and G4-positive rates increased during 2002-2003. G9-positive rates were approximately 20% during 1999-2003. G1 was predominant in Aichi Prefecture during 1971-1990, although prevalent serotypes varied from year to year (see p. 8 of this issue). G3 has been most common in Okayama and Ehime Prefectures in recent years (see p. 3&4 of this issue). G4 was predominant in Nara Prefecture during 2003-2004, followed by G3 (see p. 6 of this issue). G12 has been detected in Okayama (see p. 4 of this issue).
Although G8 and G5 have never been detected in Japan, both have been increasingly detected in tropical areas of Asia, Africa and South America (see p. 14 of this issue). Because these serotypes may be introduced into Japan one day, surveillance for serotype trends will be needed.
Future problems: Since 1986, reports of rotavirus detection have been decreasing in Japan. As testing at medical institutions became possible, fewer specimens positive for rotavirus have been submitted to PHIs.
Understanding trends in rotavirus infections, as well as collection of more precise data for infection control measures will require, under the cooperation of medical institutions, collection of appropriate samples from infectious gastroenteritis cases, detection of rotaviruses including group C, and specific testing such as group A serotyping.