Two years Bacillus cereus outbreaks: investigations and effective management of contamination in a neonatal intensive care unit

Abstract Background Bacillus cereus is an emerging cause of fulminant nosocomial bacteremia in premature infants. Here we aimed to report the successful management of two successive waves of contamination, colonization and infections caused by this pathogen in one neonatal intensive care unit (NICU). Methods This study reports all investigative, preventive, and management measures taken during these episodes (in 2023 and 2024) in a 3rd level NICU. A case was defined as an infection with B. cereus confirmed by at least one positive blood culture. Contamination was monitored by surface samples from the NICU and colonization by stool or skin samples from patients. The bacterial genomes were compared via multilocus sequence typing, core genome typing, and distance matrix. Results Between January 2021 and May 2025, B. cereus were detected in 156 surface samples within the NICU, mainly in 2023 and 2024. Three patients developed a sepsis caused by B. cereus, including 2 fatal cases. Thirty-three others patients were colonized with B. cereus during this period but none developed B. cereus sepsis. A set of structural, logistical, hygiene, and air quality optimization measures were implemented in September 2023. The environmental contamination was considered as under control in February 2024, but a resurgence was observed in April 2024. Measures to control and prevent environmental contamination in the NICU were intensified, controlling the situation by August 2024. Residual circulation persists at low levels. Analyses revealed widespread contamination including NICU equipment, air, air treatment infrastructure, linen and maintenance equipment. A pluriclonal population was described, with more than 20 different clones circulating simultaneously. The three strains isolated from blood cultures were different but each one was also identified in the NICU environment. Conclusion The detection of B. cereus, whether in carriers or in the environment, should trigger rapid investigations to identify entry points and the immediate implementation of barrier measures to protect the most vulnerable newborns. Care must be taken with respect to air treatment, laundry, and hand hygiene.