An ESBL-KPN bacteremia outbreak occurred in the 17-bed NICU of a university-affiliated hospital. This NICU, which is the referral center for the most severe cases in the region with one million population, has one isolation room with two beds and admits approximately 250 newborns each year. Staffed by three pediatricians and 35 nurses, it has a nurse-to patient ratio between 1:3 and 1:4. In 2017, the incidence of ESBL-KPN infections was 0.09/1,000 patients-days for the whole institute and 0.17/1,000 patients-days among the non-NICU children. These rates among the NICU neonates were 1.05 and 0.
Most of the neonates were premature infants who had respiratory distress, maternal risk of infections, or neonatal jaundice requiring intensive care. No routine screening for ESBL-KPN was performed before the outbreak because infections caused by this microorganism were absent in the NICU.
A case was defined as an infant either infected or colonized with ESBL-KPN. While infection was defined based on clinical and laboratory criteria according to the CDC/NHSN definitions , colonization was defined as the presence of the causative agent in the absence of relevant symptoms. The incidence was calculated as the number of new cases per 1,000 patient-days.
Survey of the outbreak
Three bacteremia cases (two in neonates) involving ESBL-KPN 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 more cases were reported in December 2017. Since the incidence (6.0/1,000 patients-days) exceeded the baseline rate, an outbreak was declared.
Accordingly, an extended infection control team (ICT) was organized to address this ESBL-KPN outbreak in the NICU. The ICT collaborated closely with the NICU team, and an outbreak survey was conducted immediately. First, the neonatal characteristics were determined. An individual record was filled out for each neonate which included demographic data, along with possible predisposing factors, gender, birth weight, age, duration of hospitalization, gestational age, Apgar score at five minutes, incubator care, use of antibiotics, mechanical ventilation, use of a central or peripheral venous catheter, location in the NICU, and presence of HAIs. Second, surveillance cultures were set up using samples from the neonates, HCWs, and the surroundings using a swab moisturized with sterile saline to identify potential reservoirs of ESBL-KPN. Active surveillance cultures (ASCs) were also set up to test the navel, axillary, inguinal, and perianal regions of the neonates (N = 17). Rectal swab specimens were also obtained from the HCWs in the NICU (N = 41) to screen for carriers. Samples from the surroundings (N = 110) and medical devices (N = 71) including incubators, total parenteral nutrition infusion pumps, glucometers, portable echocardiograms, patient monitors, respiratory therapy equipment, thermometers, stethoscopes, sinks, milk countertops, nursing carts, computer keyboards, telephones, doorknobs, and diaper scales were also cultured. To exclude the possibility of infections coming from the delivery room, samples from operation tables, incubators for emergency operations, childbirth boards, and birth measuring instruments were also cultured. Rectal swabs or stool specimens from 15 pregnant mothers who were admitted to the delivery room were cultured to rule out the vertical transmission of ESBL-KPN between January to February 2018. Third, infection control nurses monitored the compliance with hand hygiene practices among the medical personnel, and the contact precaution rates among HCWs.
Reinforced and enhanced IC program
Improvements in hand hygiene and contact precautions were reinforced for all HCWs in the NICU. We also implemented a more frequent and thorough disinfection and cleaning of medical devices, incubators, and surroundings. Group education and frequent rounds of the NICU and other areas were performed to encourage IC activities and to emphasize the seriousness of the situation.
From January to March 2018, in addition to the reinforced IC program, an enhanced IC program was established, which included cohort care of neonates and medical personnel, active surveillance cultures (ASCs), and the requirement to wear gown and glove for medical services. The ASCs involved isolation of ESBL-KPN from the skin, fecal, or perianal specimens of neonates who did not have clinical symptoms or signs of infection. The ASCs were performed every week for neonates in the NICU until March 2018.
Antibiotic susceptibility test and molecular epidemiological study
Bacteria were identified using 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 determine their genetic relatedness. Once the isolates were digested with XbaI (Roche, Basel, Switzerland) enzyme, electrophoresis was performed using CHEF MAPPER (Bio-Rad, Hercules, CA, USA). The agarose gel was stained with SYBR Gold (ThermoFisher Scientific, Waltham, MA, USA) to visualize the PFGE pattern. A dendrogram was obtained using BioNumerics (Bio-Rad) to evaluate the relationship between the strains. The similarity in PFGE patterns was interpreted according to the criteria of Tenover et al. . Seven housekeeping genes (rpoB, gapA, mdh, pgi, phoE, infB, and tonB) were amplified and sequenced to identify STs as described at http://bigsdb.pasteur.fr/klebsiella/ . The ESBL gene was amplified by PCR with known primers targeting the CTX-M-1, CTX-M-2, and CTX-M-9 genes [17, 18]. DNA sequencing was performed using the amplified PCR product, and ESBL genotypes were identified using BLAST.
Differences in the incidence rates of ESBL-KPN infections between two months were tested using a two-sample z-test, which divided the logarithm of the ratio of the incidence rates by their estimated standard error using SPSS Statistics for Windows, version 24.0 (IBM Corp., Armonk, NY, USA). A P value < 0.05 was considered to be a significant difference. Differences in compliance with guidelines for hand hygiene and contact, before and after implementation of the enhanced IC measures were tested using the Fisher's exact test.