title: Peak rotavirus activity shifted from winter to early spring in Japan.
abstract: BACKGROUND
  Since 1910, there have been many studies on acute gastroenteritis in children in Japan. These diseases, namely Kasei-shoni-kolera (pseudocholera infantum) or banshu-otosho (late autumn vomiting disease), are historically known to occur in the cooler season with a peak in November or December. Earlier we confirmed their causation by rotaviruses but found peaks in January or February from 1974 to 1981. The aim of the present study was to confirm the temporal shift in peak rotavirus activity.
  
  
  METHODS
  Under the National Epidemiological Surveillance of Infectious Diseases program from 1983 through 2003, rotavirus positive patients 0-3 years old and clinically diagnosed with "infantile vomiting and diarrhea" at sentinel clinics were examined. Fecal samples were screened by electron microscopy and/or using commercial latex agglutination kits at prefectural/municipal Public Health Institutes, and we determined the trend for the "peak" month during 21 seasons.
  
  
  RESULTS
  Peak rotavirus activity shifted gradually from January to March during the 21 consecutive seasons. The mean duration from December to the peak month (mean beginning peak duration) of the rotavirus season significantly varied among 3 periods of 7 consecutive seasons (1.7 +/- 0.5 months in 1982/1983-1988/1989, 2.3+/-0.8 months in 1989/1980-1995/1996, and 3.1 +/- 0.7 months in 1996/1997-2002/2003, respectively; P = 0.0026 by 1-way analysis of variance). This time series shift in the peak rotavirus infection was statistically significant (P = 0.0003 for trend).
  
  
  CONCLUSIONS
  Our findings confirmed that the temporal trend in peak rotavirus activity in Japan has shifted gradually from winter to early spring for unknown reasons.
authors.affiliation: Division of Public Health, Department of Infectious Disease Control and International Medicine, Niigata University, Graduate School of Medical and Dental Sciences, Niigata City, Niigata, Japan. hsuzuki@med.niigata-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Takatsugu
authors.initials: T
authors.lastname: Sakai
authors.forename: Naohito
authors.initials: N
authors.lastname: Tanabe
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Okabe
mesh_terms: D017677:Age Distribution; D002675:Child, Preschool; D003968:Diarrhea, Infantile / Q000453:epidemiology / Q000821:virology; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D005260:Female; D005759:Gastroenteritis / Q000453:epidemiology / Q000821:virology; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D007223:Infant; D007564:Japan / Q000453:epidemiology; D008297:Male; D011159:Population Surveillance; D011336:Probability; D012307:Risk Factors; D012401:Rotavirus / Q000302:isolation & purification*; D012400:Rotavirus Infections / Q000175:diagnosis* / Q000453:epidemiology*; D012621:Seasons; D012720:Severity of Illness Index; D017678:Sex Distribution