title: Incidence and geographical distribution of sudden infant death syndrome in relation to content of nitrate in drinking water and groundwater levels.
abstract: BACKGROUND
  Previous studies indicate that the enteral bacterial urease is inhibited in victims of sudden infant death syndrome (SIDS). One possible inhibitor of this bacterial activity is nitrate. If ambient pollution by nitrate is involved in the etiology of SIDS only a fraction of the nitrate concentration not infrequently found in drinking water would be enough for this inhibition.
  
  
  METHODS
  Occurrence of SIDS (n = 636) in Sweden during the period 1990 through 1996 were analysed regarding geographical and seasonal distribution in relation to the nitrate concentration in drinking water and changes in the groundwater level.
  
  
  RESULTS
  Both the birth rate and the incidence of SIDS decreased during the study period. One quarter of the municipalities constituting 11% of the population had no cases, the maximum incidence being 6.5 per 1000 live births. Seasonality: The northernmost parts of the country had its highest incidence when the rest of the country had its lowest incidence, and the occurrence of individual deaths was associated with the recharge of groundwater which increases its nitrate content. The local incidence of SIDS was correlated (rs = 0.34-0.87) to maximally recorded concentrations of nitrate in drinking water.
  
  
  CONCLUSIONS
  The seasonal distribution of SIDS was widely different from the south to the north of the country and seems to be associated with differences in the groundwater level changes subsequent to precipitation, frost penetration, and melting of snow. Use of drinking water with high peak concentrations or great variations in nitrate concentration was correlated to the incidence of SIDS.
authors.affiliation: Dept of Anesthesiology and Intensive Care, Uppsala University Hospital, SE-751 85 Uppsala, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: George
authors.forename: L
authors.initials: L
authors.lastname: Wiklund
authors.forename: M
authors.initials: M
authors.lastname: Aastrup
authors.forename: J
authors.initials: J
authors.lastname: Pousette
authors.forename: B
authors.initials: B
authors.lastname: Thunholm
authors.forename: T
authors.initials: T
authors.lastname: Saldeen
authors.forename: L
authors.initials: L
authors.lastname: Wernroth
authors.forename: B
authors.initials: B
authors.lastname: Zarén
authors.forename: L
authors.initials: L
authors.lastname: Holmberg
mesh_terms: D006801:Humans; D015994:Incidence; D007223:Infant; D009566:Nitrates / Q000032:analysis*; D012044:Regression Analysis; D013398:Sudden Infant Death / Q000453:epidemiology*; D013548:Sweden / Q000453:epidemiology; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis; D014881:Water Supply
chemical_list: D009566:Nitrates; D014874:Water Pollutants, Chemical; D014867:Water