title: Estimating the under-reporting of norovirus illness in Germany utilizing enhanced awareness of diarrhoea during a large outbreak of Shiga toxin-producing E. coli O104:H4 in 2011--a time series analysis.
abstract: BACKGROUND
  Laboratory-confirmed norovirus illness is reportable in Germany since 2001. Reported case numbers are known to be undercounts, and a valid estimate of the actual incidence in Germany does not exist. An increase of reported norovirus illness was observed simultaneously to a large outbreak of Shiga toxin-producing E. coli O104:H4 in Germany in 2011--likely due to enhanced (but not complete) awareness of diarrhoea at that time. We aimed at estimating age- and sex-specific factors of that excess, which should be interpretable as (minimal) under-reporting factors of norovirus illness in Germany.
  
  
  METHODS
  We used national reporting data on laboratory-confirmed norovirus illness in Germany from calendar week 31 in 2003 through calendar week 30 in 2012. A negative binomial time series regression model was used to describe the weekly counts in 8∙2 age-sex strata while adjusting for secular trend and seasonality. Overall as well as age- and sex-specific factors for the excess were estimated by including additional terms (either an O104:H4 outbreak period indicator or a triple interaction term between outbreak period, age and sex) in the model.
  
  
  RESULTS
  We estimated the overall under-reporting factor to be 1.76 (95% CI 1.28-2.41) for the first three weeks of the outbreak before the outbreak vehicle was publicly communicated. Highest under-reporting factors were here estimated for 20-29 year-old males (2.88, 95% CI 2.01-4.11) and females (2.67, 95% CI 1.87-3.79). Under-reporting was substantially lower in persons aged <10 years and 70 years or older.
  
  
  CONCLUSIONS
  These are the first estimates of (minimal) under-reporting factors for norovirus illness in Germany. They provide a starting point for a more detailed investigation of the relationship between actual incidence and reporting incidence of norovirus illness in Germany.
authors.affiliation: Department for Infectious Disease Epidemiology, Robert Koch Institute, Seestraße 10, 13353 Berlin, Germany. BernardH@rki.de.
authors.forename: Helen
authors.initials: H
authors.lastname: Bernard
authors.forename: Dirk
authors.initials: D
authors.lastname: Werber
authors.forename: Michael
authors.initials: M
authors.lastname: Höhle
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D017250:Caliciviridae Infections / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D003967:Diarrhea / Q000453:epidemiology; D004196:Disease Outbreaks; D062665:Epidemiological Monitoring; D004927:Escherichia coli Infections / Q000453:epidemiology; D005260:Female; D005759:Gastroenteritis / Q000453:epidemiology*; D005858:Germany / Q000453:epidemiology; D006463:Hemolytic-Uremic Syndrome / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D029322:Norovirus; D022621:Shiga Toxin / Q000032:analysis; D054323:Shiga-Toxigenic Escherichia coli; D055815:Young Adult
chemical_list: D022621:Shiga Toxin