Enterobacter sakazakii Infection and Powdered Infant Formulas

On April 9, 2002, the United States Food and Drug Administration (USFDA) issued an alert to US Health Care Professionals regarding the risk associated with Enterobacter sakazakii infections among neonates fed milk-based, powdered infant formulas. Historically, there have been several small E. sakazakii outbreaks reported among infants fed milk-based, powdered formula products from various manufacturers. In addition to powdered milk-based formulas, powdered human milk fortifiers may also pose a hazard.

E. sakazakii is a motile peritrichous, gram-negative rod from the family Enterobacteriaceae. This organism used to be known as a "yellow pigmented Enterobacter cloacae" until 1980, when it was introduced as a new species based on differences in DNA-DNA hybridization, biochemical reactions, and antibiotic susceptibility. E. sakazakii is a rare, but life-threatening cause of neonatal meningitis, sepsis, and necrotizing enterocolitis. In general, the reported case-fatality rate varies from 40-80 % among newborns diagnosed with this type of severe infection. The type of meningitis caused by E. sakazakii may lead to cerebral abscess or infarction with cyst formation and severe neurologic impairment.

There is still a paucity of information on the ecology of this bacterium. However, studies have shown that this organism can be isolated from hospital and processing plant environments. Reports have also suggested a correlation between E. sakazakii infection and powdered infant formulas. Similarly, it has been reported that premature infants and those with underlying medical conditions may be at highest risk for developing an E. sakazakii infection.

Several outbreaks of E. sakazakii, in Neonatal Intensive Care Units (NICUs), have been reported worldwide including countries such as England, Netherlands, Greece, US and Canada. In Canada, two incidents of neonatal meningitis caused by E. sakazakii were reported in two Canadian hospitals (1990, 1991). It should be noted that healthy infants may not always be immune to E. sakazakii infections. It has been reported that in Iceland, a healthy, full-term, newborn infant became ill prior to hospital discharge and suffered permanent neurological sequelae as a result of an E. sakazakii infection.

Health Canada is drawing attention to the fact that powdered infant formulas are not commercially sterile products. Unlike liquid formulas, which are subjected to sufficient heat to render them commercially sterile, powdered infant formulas are not processed at high enough temperatures for sufficient time to achieve commercial sterility. Ready-to-use liquid infant formulas are available only in a commercially sterile form and indicated for premature or low-birth weight infants. However,"transition" infant formulas which are used for premature or low-birth weight infants after hospital discharge, may be either powdered or liquid. Human milk fortifiers which are added to pre-term breast milk are also available in powdered or liquid forms. A number of formulas, including formulas for infants with metabolic conditions are only available in powdered form. Powdered soy-based infant formulas may also become contaminated with E. sakazakii through improper cleaning of production lines and may, therefore, pose a safety hazard.

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