Maternal Colonization, Perinatal Exposure, and Neonatal Acquisition of Resistant Enterobacterales.

Background: Enterobacterales with ampicillin (AmpR-E) and ceftriaxone resistance (CefR-E) are globally prevalent. Perinatal transmission and infections with CefR-E strains are associated with higher mortality, morbidity, and health care costs. This study estimated the rate of gut colonization of AmpR-E and CefR-E in healthy birthing parent-infant dyads in Chicago and investigated the genetic characteristics of CefR-E. Methods: Pregnant persons anticipating vaginal birth at 2 Chicago-area hospitals were enrolled. Pregnancy and birth history were obtained. Maternal vaginal and rectal swabs and infant stool samples were collected and screened for resistance. CefR-E isolates underwent whole-genome sequencing analysis. Results: Birthing parent-infant dyads were enrolled and 293 parent, and 261 infant samples were collected (July 2020-January 2023). After exclusionary criteria, parental AmpR-E colonization was 91% (216/238), and infant AmpR-E colonization was 76% (158/208). The rate of parental and infant CefR-E colonization was 12% (28/238) and 7% (15/208), respectively. Estimated perinatal transmission of CefR-E was 17% (4/24). Race was the only clinical variable significantly associated with parental CefR-E colonization (higher Asian, decreased White race). Birthing parent age and type of infant nutrition (breastmilk) were significantly associated with decreased infant AmpR-E colonization ( Conclusions: This study demonstrates that a sizable percentage of healthy pregnant persons are colonized with AmpR-E and CefR-E in the United States, a higher burden than previously reported for high-income countries. Enterobacterales appear adept in perinatal transmission, with a significant proportion of infants born to colonized pregnant persons harboring CefR-E in the first week of life.