Abstract :
BACKGROUND: Enterobacter sakazakii (E. sakazakii), a gram-negative bacillus of the Enterobacteriacae family, is a rare cause of meningitis, bacteremia, and necrotizing enterocolitis in infants. The population at particular risk is infants born prematurely, of low birthweight, or with compromised immunity. In 2004, an outbreak investigation was initiated in our neonatal intensive care unit (NICU) when a 5-day-old premature baby was found to be growing E. sakazakii in blood culture. The index case (Baby A) was born at 33 weeks gestation and admitted to NICU for observation. She received few medications and was fed with a combination of expressed breastmilk and infant formula. Five days after birth, Baby A became unwell. Despite treatment, she suffered progressive neurological damage and died on day 18.
METHODS: The organism identification was confirmed and background microbiology isolate rates ascertained: 0-2 isolates per year were found, but no isolate had originated from NICU. A review of international literature revealed an association between E. sakazakii infection in neonates and the use of powdered infant formula. The cohort of neonates present in NICU had feces samples collected for culture along with demographic and risk factor/exposure data. A case patient was any neonate diagnosed with E. sakazakii infection (confirmed or suspected) or colonization who had been in NICU during the 5-day study period. Samples of medications, water, powdered infant formula, and breastmilk and samples from surfaces and equipment in formula preparation areas were among environmental specimens cultured. All aspects of infant formula preparation and use were reviewed, along with patient care practices within NICU. Use of sterile “ready-to feed” formula was implemented.
RESULTS: Of 24 babies screened, four babies were identified as being colonized with E. sakazakii. None became clinically unwell. Two types of powdered infant formula were positive for E. sakazakii. Pulsed-field gel electrophoresis (PFGE) analysis found that E. sakazakii isolated from the index case, all four colonized cases, and one batch of powdered infant formula were all indistinguishable. The index case and two colonized babies had received this type of formula.
CONCLUSIONS: Powdered infant formula is not a sterile product and may be contaminated with E. sakazakii. International recommendations advocating the use of sterile liquid formula for NICU babies should be widely publicized.
