title: Incidence and etiology of hemolytic-uremic syndrome in children in Norway, 1999-2008--a retrospective study of hospital records to assess the sensitivity of surveillance.
abstract: BACKGROUND
  Public awareness of hemolytic-uremic syndrome (HUS), especially related to Shiga toxin-producing Escherichia coli (STEC), has increased in Europe in recent years; accentuated in Norway by a national outbreak in 2006 and in a European context especially by the 2011 outbreak originating in Germany. As STEC surveillance is difficult due to diagnostic challenges in detecting non-O157 infections, surveillance of HUS can be used to indicate the burden of STEC infection. Until 2006, notification of HUS to the Norwegian Communicable Disease Surveillance System (MSIS) was based on microbiologically confirmed infection with enterohemorrhagic Escherichia coli (EHEC), humanpathogenic STEC. In 2006, diarrhea-associated HUS (D(+)HUS) was made notifiable based on clinical criteria alone. The incidence and etiology of HUS in children in Norway has not previously been described.
  
  
  METHODS
  In order to assess the sensitivity of STEC and D+HUS surveillance and describe the incidence and etiology of HUS in children in Norway, we conducted a nationwide retrospective study collecting data from medical records from pediatric departments for the period 1999-2008 and compared them with data from MSIS. Descriptive statistics are presented as proportions, median, average and mean values with ranges and as incidence rates, calculated using population numbers provided by official registries.
  
  
  RESULTS
  Forty-seven HUS cases were identified, corresponding to an average annual incidence rate of 0.5 cases per 100,000 children. Diarrhea-associated HUS was identified in 38 (81%) cases, of which the median age was 29 months, 79% were <5 years of age and 68% were girls. From 1999 to 2006, thirteen more diarrhea-associated HUS cases were identified than had been notified to MSIS. From the change in notification criteria to 2008, those identified corresponded to those notified. STEC infection was verified in 23 (49%) of the HUS cases, in which O157 was the most frequently isolated sporadic serogroup.
  
  
  CONCLUSIONS
  Our results show that the incidence of HUS in children in Norway is low and suggest that D+HUS cases may be underreported when notification requires microbiological confirmation. This may also indicate underreporting of STEC infections.
authors.affiliation: Department of Infectious Disease Epidemiology, Norwegian Institute of Public Health (Nasjonalt Folkehelseinstitutt), Postboks 4404 Nydalen, Oslo NO 0403, Norway. gautereier@gmail.com.
authors.forename: Gaute Reier
authors.initials: GR
authors.lastname: Jenssen
authors.forename: Eirik
authors.initials: E
authors.lastname: Hovland
authors.forename: Anna
authors.initials: A
authors.lastname: Bjerre
authors.forename: Hans-Jacob
authors.initials: HJ
authors.lastname: Bangstad
authors.forename: Karin
authors.initials: K
authors.lastname: Nygard
authors.forename: Line
authors.initials: L
authors.lastname: Vold
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003141:Communicable Diseases / Q000453:epidemiology; D003967:Diarrhea / Q000453:epidemiology / Q000382:microbiology; D004196:Disease Outbreaks / Q000706:statistics & numerical data; D004927:Escherichia coli Infections / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D006463:Hemolytic-Uremic Syndrome / Q000453:epidemiology* / Q000235:genetics / Q000382:microbiology; D006753:Hospital Records; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D009664:Norway / Q000453:epidemiology; D062486:Public Health Surveillance; D012189:Retrospective Studies; D054323:Shiga-Toxigenic Escherichia coli / Q000302:isolation & purification*