Background: Listeriosis is a rare but serious infectious disease caused by Listeria monocytogenes (LM) and predominantly transmitted through contaminated food. Moreover, 15% of listeriosis cases in the United States are pregnancy associated; nosocomial neonatal transmission in hospitals is extremely rare. In July 2018, the California Department of Public Health (CDPH) was notified of 4 patients, a mother–neonate pair and twin neonates, with listeriosis at the same hospital. The CDPH and San Diego County Health and Human Services Agency initiated an investigation to determine transmission and prevent additional infections. Methods: We reviewed medical records of the neonates and their mothers, interviewed the mothers with a detailed food exposure questionnaire, interviewed healthcare personnel (HCP), and performed an infection control assessment of the neonatal intensive care unit (NICU). CDPH performed whole-genome sequencing (WGS) on LM isolates that were then analyzed by whole-genome multilocus sequence typing (wgMLST) by the Centers for Diseases Control and Prevention (CDC) to assess relatedness in PulseNet, a public health laboratory database. The CDC also performed testing for LM on formalin-fixed placentas from the mother of the twins. Results: During a 1-week period, 4 patients with LM were identified at the hospital. A mother was admitted at 31 weeks gestation with acute abdominal and back pain that progressed with precipitous vaginal delivery and postpartum sepsis. Her neonate was resuscitated, transported to the NICU, underwent a sepsis evaluation, received antibiotics, and was transferred to another hospital within 6 hours. Maternal blood, placenta, and neonatal blood cultures grew LM. Twin neonates, born to an asymptomatic mother and present in the NICU during the index neonate’s stay, developed acute infection 4 and 6 days after the index neonate’s transfer; blood cultures confirmed LM. The LM isolates from the 4 patients were indistinguishable by wgMLST and were not related to other PulseNet isolates. LM was not detected in the twin placentas. There were no common food exposures between the mothers. At least 1 common HCP cared for all 3 neonates. Infection control lapses included lack of proper hand hygiene during the index neonate’s resuscitation and potentially after cleaning and disinfection of the neonate’s incubator. Conclusions: This report provides supportive evidence that nosocomial transmission of LM can occur during a brief NICU stay due to lapses in infection control practices. Strict adherence to standard precautions in the delivery room and NICU is imperative to prevent cross transmission.

Disclosures: None

Funding: None