The Age of Necrotizing Enterocolitis Onset: An Application of Sartwell’s Incubation Period Model

OBJECTIVES: Model age of necrotizing enterocolitis (NEC) onset applying Sartwell’s model of incubation periods, and examine its relationship to gestational age (GA). STUDY DESIGN: Retrospective chart review of St. Louis Children’s Hospital neonates diagnosed with NEC (≥ Bell’s stage II) from 2004 to 2008, inclusive. RESULTS: The relationship between age of NEC (N=84 cases) onset and GA best fits a non-linear model, with infants ≤ 28 weeks having a disproportionately longer time to onset than older GA groups and explained 50.3% of the variability in age of NEC onset. Additional clinical variables provided no improvement in explaining age of NEC onset. Application of Sartwell’s model to age of NEC onset proved a good fit, when birth is used as the common exposure episode, and age is the equivalent of the incubation period. CONCLUSION: The relationship between day of NEC diagnosis and GA is non-linear, with lower GA infants having disproportionately longer time to onset. Despite these GA differences, the fit to Sartwell’s model for incubation periods model is consistent with NEC being a consequence of an event that occurs at or soon after birth.