The ESBL-KPN outbreak occurred in the 17-bed NICU of a university-affiliated hospital. The NICU is staffed by three pediatricians and 35 nurses. Approximately 250 newborns are admitted to the NICU each year and there is one isolation room with two beds. The nurse-to-patient ratio was between 1:3 and 1:4. The infection control team (ICT) of our institute collaborated closely with the NICU team.
Incidence and outbreak
A neonate who tested positive for ESBL-KPN from any specimen and was admitted to the NICU for ≥48 h was defined as a positive case. The incidence was calculated as new cases per 1,000 patient-days. If the incidence exceeded the upper limit of control (mean + 2 SD), it was defined as an outbreak. HAI was defined according to CDC/NHSN definitions .
Three cases of ESBL-KPN HAI were observed in August and September, 2017. Considering the high risk of spread in the NICU, a reinforced conventional IC program was initiated in November, 2017. However, three cases of bacteremia occurred in December, 2017. Accordingly, an extended ICT was organized to address this ESBL-KPN outbreak in the NICU.
Survey of the outbreak
When the incidence density rate of HAI increased to 6.0 in December, 2017 (Fig. 1), a survey was initiated immediately. First, neonatal characteristics were determined, including birth week and weight, birth method, route of admission, previous antibiotic use, microbiological data, start date of isolation, location, and presence of HAI. IRB permission was not required from the ethics board of our institute because this was a formal IC activity to resolve the outbreak.
Second, the behavior of medical personnel was monitored, including hand hygiene and contact precaution rates. Rectal swab specimens were obtained from medical personnel (N = 41) to screen carriers as well as from neonates (N = 15).
Third, the disinfection of medical devices and environmental cleaning were promoted. Samples were obtained to rule out transmission via medical devices (N = 71), such as thermometers, stethoscopes, or patient monitoring systems as well as environmental sources (N = 110), such as incubators or surroundings.
Reinforced and enhanced IC program
Improvements in hand hygiene and contact precaution were reinforced for all medical personnel working in the NICU. More frequent and thorough disinfection and cleaning was implemented for medical devices, incubators, and surroundings. Group education and frequent rounding were performed to encourage IC activities and to share the seriousness of the situation.
An enhanced IC program was established, including cohort care of neonates and medical personnel, active surveillance cultures (ASC), and universal gown and glove wearing for medical services, in addition to the reinforced IC program from January to March, 2018. ASC involved the isolation of ESBL-KPN from skin, fecal, or perianal specimens from a neonate who did not have clinical symptoms or signs of infection. ASC was performed every week for neonates in the NICU until March, 2018.
Antibiotic susceptibility test and molecular epidemiological study
Bacteria were identified by MALDI-TOF MS (bioMérieux; Durham, NC, USA) and antibiotic susceptibility tests were performed by the broth microdilution method using the Vitek-2 system (bioMérieux, Marcy l'Etoile, France). Isolates of KPN showing ESBL resistance were analyzed by PFGE and multi-locus sequence typing to understand molecular relatedness. Once the isolates were digested with XbaI (Roche, Basel, Switzerland) enzyme, electrophoresis was performed using CHEF MAPPER (Bio-Rad, Hercules, CA, USA). Agarose gel was stained with SYBR Gold (ThermoFisher Scientific, Waltham, MA, USA) to yield a PFGE pattern. A dendrogram was obtained using BioNumerics (Bio-Rad) to evaluate the relationships between the strains. Seven housekeeping genes (rpoB, gapA, mdh, pgi, phoE, infB, and tonB) were amplified and sequenced to identify STs as described in Institute Pasteur http://bigsdb.pasteur.fr/klebsiella/ .
ESBL was amplified by PCR with known primers targeting the CTX-M-1, CTX-M-2, and CTX-M-9 groups [15, 16]. DNA sequencing was performed using the amplified PCR product and ESBL genotypes were identified using BLAST.
Chi-square tests were used to compare the incidence of HAI and the compliance rates for hand hygiene and contact precaution before and after enhanced IC measures using SPSS Statistics for Windows, version 24.0 (IBM Corp., Armonk, NY, USA). A P value < 0.05 indicates a significant difference.