title: Seasonal variation in the incidence of necrotizing enterocolitis.
abstract: BACKGROUND
  Necrotizing enterocolitis (NEC) has been reported to occur in a sporadic manner and in clusters of cases. We hypothesized that variations in the incidence of NEC were random, without clustering. In order to define the pattern of NEC in the United States, we analyzed the Pediatric Health Information System (PHIS) database to evaluate whether NEC cases are distributed randomly or exhibit temporal clustering or periodicity.
  
  
  METHODS
  After obtaining IRB approval, we queried the PHIS database for all patients with NEC (ICD-9 code of 777.5) over a 13-year period. Sixteen children's hospitals were studied, and individual institutional and aggregate data were reviewed. Fisher's Kappa and Bartlett's Kolmogorov-Smirnov tests were used to identify periodicity.
  
  
  RESULTS
  During the study interval, there were 2,93,076 neonatal admissions, and 4,559 (1.6%) infants were diagnosed with NEC. Statistical analysis demonstrates a periodicity of 6 months in the occurrence of NEC. Fisher's Kappa was 16.924 and Bartlett's Kolmogorov-Smirnov was 0.281, which translates to a P value of <0.0001.
  
  
  CONCLUSIONS
  On the basis of a national database analysis it appears a temporally non-random distribution of NEC cases does exist.
authors.affiliation: The Children's Mercy Hospital, Kansas City, USA. clsnyder@gmail.com
authors.forename: Charles L
authors.initials: CL
authors.lastname: Snyder
authors.forename: Matt
authors.initials: M
authors.lastname: Hall
authors.forename: Vidya
authors.initials: V
authors.lastname: Sharma
authors.forename: Shawn D
authors.initials: SD
authors.lastname: St Peter
mesh_terms: D016208:Databases, Factual; D020345:Enterocolitis, Necrotizing / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D010343:Patient Admission / Q000706:statistics & numerical data; D010507:Periodicity; D014481:United States / Q000453:epidemiology