Definition, Incidence, and Epidemiology
NEC is best defined along a continuum from suspected cases to infants with advanced disease. Suspected cases present with nonspecific signs and may reflect feeding intolerance, sepsis, or GI bleeding caused by stress or other factors. In 1978, Bell et al presented a system for the uniform clinical staging of neonates with NEC. Later, other authors expanded these stages to include systemic, GI, and radiographic features[10,11] ( Table 1 ). Use of a staging system with consistent disease definitions improves the clinician's ability to compare cases and interpret research findings more accurately.
The incidence of NEC varies. It is stated most often as 1% to 7% of all neonatal intensive care unit (NICU) admissions, or 1 to 3 per 1,000 live births, and it occurs equally in males and females.[1,2,3,4] Most published reports calculate NEC incidence for an individual institution over a specified time. That information is then expressed as a percentage of all NICU admissions with NEC. Further extrapolation is often made to the number of cases per 1,000 live births at the institution. The mortality rate for NEC is estimated to be 11.5 to 12.3 per 100,000 infant deaths, greatly exceeding that of other GI surgical disorders.
Institutional, regional, and gestational age variations in prevalence exist. Preterm infants account for 70% to 90% of total NEC cases, the more preterm the infant the higher the risk.[2,3] By 36 weeks of gestation, there is a sharp decrease in incidence, supporting the hypothesis that GI maturation plays an important role in the development of NEC.[1,2,4]
In 2001, the National Institute of Child Health and Human Development (NICHD) Neonatal Research Network reported (from a data set of 14 centers) an overall incidence of proven NEC of 7% in very low-birth-weight infants (VLBW) (401 to 1,500 g). The incidence increased to 15% for infants between 501 to 600 g. Although the survival of the smallest preterm neonates has improved over time, NEC-related morbidity remains unchanged.
A report from Australia suggests that NEC incidence in preterm neonates born at <29 weeks gestation is higher in hospitals with in-house surgical facilities compared with hospitals without these resources, despite statistically similar mortality rates. The Vermont Oxford Network database examined information for close to 20,000 neonates (501 to 1,500 g) from 196 hospitals, to find that the presence of intrauterine growth restriction increased the risk of NEC. The true incidence of NEC may be clouded by institutional practices or differences in specific patient and gestational age characteristics.
Adv Neonatal Care. 2003;3(3) © 2003 W.B. Saunders
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