In the context of a 3-month extended-spectrum beta-lactamase-producing Klebsiella pneumonia (ESBL-KP) outbreak in a neonatal care center (NCC), hygiene practices and hospital environment were investigated. ESBL-KP strains isolated from patients and environment were compared by molecular typing. The density of incidence of multi-drug-resistant bacteria (MDRB) was calculated from January 2014 to September 2016. The 3-month ESBL-KP outbreak involved 19 patients. Clinical strains from the 19 patients displayed the same molecular profile between them, and with a strain isolated from an incubator after cleaning. Furthermore, 52.4% of incubator mattresses were positive for diverse pathogens. Hygiene practices were acceptable except for external practitioners and parents. In addition to classical infection control (IC) measures, the replacement of mattresses and the improvement of incubators disinfection stopped the outbreak. The protocol of disinfection was revised and microbiological control was implemented. A significant decrease of MDRB incidence was concomitant (p value = 0.03219) but 3 months later, MDRB incidence increased again.Conclusion: This investigation highlighted incubators and mattresses as critical materials associated to infectious risk in NCC. NCC and IC teams should implement efficient protocol for incubators disinfection and monitoring. What is Known: • Environment in neonatal intensive care units is often suspected as reservoir for Enterobacteriaceae outbreaks but is scarcely investigated. • Incubators and mattresses offer wet and warm conditions suitable for pathogens multiplication, but microbiological survey is not performed routinely for assessing bacterial contamination. What is New: • Incubators and mattresses serve as reservoir for pathogens and relay in outbreak. • An infection control protocol associating efficient disinfection and microbiology analysis is proposed.