Necrotizing enterocolitis in infants born in Japan and born to Japanese mothers in California: a retrospective cohort study

Abstract Objectives: There is a variation in the incidence of necrotizing enterocolitis (NEC) among countries. To investigate the influence of ethnicity, NEC incidents were compared between Japan and California. Study Design: A retrospective cohort study was conducted using neonatal databases in Japan and California, including infants between 2008 and 2019 at 22-29 gestational weeks. Infants born in Japan (JP) were compared to infants born in California to mothers born in Japan (JP-J), to mothers with Japanese ethnicity born outside Japan (JP-CA), and to non-Hispanic White mothers (NHW-CA). Results: Each cohort consisted of 52,049, 115, 226, and 12,275 infants, respectively. Unadjusted NEC incidences were significantly lower in JP (1.7% vs. 4.4% JP-J+JP-C, and 3.3% NHW-CA, respectively; p<0.01). After background adjustment, odds ratios in JP-J, JP-CA, and NHW-CA vs. JP were 3.0 (1.2-7.8), 2.9 (1.5-5.8), and 2.0 (1.6-2.5), respectively. Conclusions: The NEC incidence variation could not be explained solely based on ethnic background.