Necrotizing enterocolitis (NEC) is a serious gastrointestinal disease that occurs primarily in preterm infants. The disease is characterized by the rapid onset of intestinal inflammation and, in severe cases, can lead to intestinal necrosis and multiorgan dysfunction that results in death. Since the 1950s, when neonatal intensive care was introduced at many centers around the world with survival of very low–birth-weight (VLBW) infants, NEC has been reported as a complication of premature birth. It remains the most common gastrointestinal complication in preterm infants, and is a major cause of morbidity and mortality in neonates, accounting for 10% of deaths in the neonatal intensive care unit (NICU). Reports from the United States, the United Kingdom, Sweden, and the Netherlands indicate that NEC is increasing as a cause of death, as survival from lung disease has improved for preterm infants.
Incidence and Recent Trends
The incidence of NEC varies among studies, depending on the population studied, case definition, and geographic region. Among a large network of NICUs in the United States encompassing 58,555 infants weighing 500 to 1500 g, the combined incidence of medical and surgical NEC was 3.9% in 2013 (2.6% medical NEC, 1.2% surgical), which had significantly declined from 6.6% in 2007. Similarly, the incidence of NEC in the Neonatal Research Network for infants with birthweights between 401 and 1500 g and born at 22 to 28 weeks’ gestation decreased from 13% in 2008 to 9% in 2012 (P < 0.01). This figure had previously increased between 1993 and 2008. The incidence of Bell stage 2 or 3 NEC for infants who survived for more than 12 hours after birth ranged from 15% at 23 weeks’ gestation to 8% at 28 weeks’ gestation. In a recent population-based cohort in the United Kingdom, the incidence of severe NEC was 3.2% (95% confidence interval [CI], 2.9–3.4; Fig. 60-1).
Incidence and case-fatality rates of necrotizing enterocolitis (NEC) by gestational age. Data from a population-based cohort of 118,073 infants in the United Kingdom. No NEC cases observed for infants at 22 weeks’ gestation (n = 12).
The age at onset of NEC varies depending on the gestational age of the infant. More immature preterm infants present later in the hospital course compared to more mature preterm or term infants. NEC in term infants typically presents early, with a reported mean age of onset of 4 days. This observation has suggested a potential developmental window of highest disease risk, although there is substantial variation in both the postnatal age and postmenstrual age (PMA) at onset, even among distinct gestational age subgroups. Among infants less than 32 weeks’ gestation who required surgery for NEC, the PMA of onset was a median of 30.5 weeks ...