Seasonal variation in the incidence of necrotizing enterocolitis

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. 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. 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. On the basis of a national database analysis it appears a temporally non-random distribution of NEC cases does exist.