title: Population-based study showed that necrotising enterocolitis occurred in space-time clusters with a decreasing secular trend in Sweden.
abstract: OBJECTIVE
  This study investigated space-time clustering of neonatal necrotising enterocolitis over three decades.
  
  
  METHODS
  Space-time clustering analyses objects that are grouped by a specific place and time. The Knox test and Kulldorff's scan statistic were used to analyse space-time clusters in 808 children diagnosed with necrotising enterocolitis in a national cohort of 2 389 681 children born between 1987 and 2009 in Sweden. The municipality the mother lived in and the delivery hospital defined closeness in space and the time between when the cases were born - seven, 14 and 21 days - defined closeness in time.
  
  
  RESULTS
  The Knox test showed no indication of space-time clustering at the residential level, but clear indications at the hospital level in all the time windows: seven days (p = 0.026), 14 days (p = 0.010) and 21 days (p = 0.004). Significant clustering at the hospital level was found during 1987-1997, but not during 1998-2009. Kulldorff's scan statistic found seven significant clusters at the hospital level.
  
  
  CONCLUSIONS
  Space-time clustering was found at the hospital but not residential level, suggesting a contagious environmental effect after delivery, but not in the prenatal period. The decrease in clustering over time may reflect improved routines to minimise the risk of contagion between patients receiving neonatal care.
authors.affiliation: Department of Pediatrics, Institution of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Amanda
authors.initials: A
authors.lastname: Magnusson
authors.affiliation: Division of Radiology, Department of Medical and Health Sciences, Faculty of Health Sciences, Linköping University, Linköping, Sweden.|Department of Radiology in Linköping, County Council of Östergötland, Linköping, Sweden.
authors.forename: Margareta
authors.initials: M
authors.lastname: Ahle
authors.affiliation: Department of Pediatrics, Institution of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Diana
authors.initials: D
authors.lastname: Swolin-Eide
authors.affiliation: Department of Pediatrics, Institution of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Elfvin
authors.affiliation: Department of Surgery, County Hospital Ryhov, Jönköping, Sweden.
authors.forename: Roland E
authors.initials: RE
authors.lastname: Andersson
mesh_terms: D015331:Cohort Studies; D020345:Enterocolitis, Necrotizing / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D013548:Sweden / Q000453:epidemiology
keywords: Cluster analysis; Necrotising enterocolitis; Neonatal care; Precipitating contagion; Preterm infant