Food Safety Focus (28th Issue, November 2008) – Incident in Focus
Enterobacter sakazakii in Powdered Infant Formula
Reported by Dr. Ken Chong, Scientific Officer,
Risk Assessment Section, Centre for Food Safety
In September 2008, the media reported that apart from melamine, Enterobacter sakazakii (also called Cronobacter species) was detected in powdered infant formula (PIF) from the Sanlu brand. In this article, we shall focus on this bacterium and relevant Food and Agriculture Organization (FAO) / World Health Organization (WHO) advice on safe preparation and handling of PIF.
Enterobacter sakazakii and Infection in Infant
Enterobacter sakazakii is a gram-negative, non-sporeforming bacterium with optimum growing temperatures ranging from 37℃ to 43℃. It is a pathogen that generally causes disease only in people with weakened immune systems. There is emerging public health concern of this bacterium because it can cause rare but fatal infections in infants (i.e. children < one year old).
The bacterium can cause invasive infections (e.g. blood or brain infections) in infants. In particular, neonates ( ≤ 28 days old), infants less than two months of age, pre-term infants, low-birth-weight infants (< 2.5 kg) and infants with weakened immunity are at greatest risk. One of the possible factors for this may be due to the stomach of newborns, especially of premature babies, is less acidic than that of adults, which may contribute to the survival of E nterobacter sakazakii in infants.
The Germ in the Powdered Infant Formula
Despite the source of Enterobacter sakazakii is not known in many cases of infant infection, increasing number of reports have suggested PIF as the vehicle for Enterobacter sakazakii, which can also be found in the manufacturing environment. Even low level of the bacterium in PIF can lead to infection.
Although the bacterium does not grow in dry PIF, it can survive for long periods. Reconstituted PIF can provide favourable environment for growth of the bacterium when it is held at room temperature (i.e. above 4℃), particularly for extended period.
FAO/WHO Assessments on Enterobacter sakazakii
The Joint FAO/WHO Expert Meeting on Microbiological Risk Assessment (JEMRA) has evaluated the risk-reduction strategies for Enterobacter sakazakii in PIF. As contamination can occur at manufacturing and preparation stages, appropriate control measures should be applied during the manufacturing process as well as during and after reconstitution.
JEMRA concluded that controlling intrinsic contamination (i.e. contamination in PIF before opening) would help to decrease the risk for the bacterium, which relies on effective implementation of preventive measures by manufacturers. These include strengthening measures that further minimize entry of microorganisms and avoid their multiplication, such as exclusion of water from the processing environment to the extent possible and feasible. In addition, it is also required to implement monitoring and environmental management programmes, which cover all relevant elements including the processing environment, product contact surfaces and finished product.
On the other hand, JEMRA evaluated different scenarios for preparation and handling of PIF and recommended several practices that can help reduce the risk. Reconstitution of PIF with water that is no less than 70℃ can significantly inactivate Enterobacter sakazakii. To limit bacterial growth, the time from preparation to consumption should be minimised, i.e. consume the feeds within two hours after preparation; feeds prepared in advance are required to cool immediately and stored at or below 4℃ as well as re-warmed for no longer than 15 minutes for consumption within 24 hours of preparation; and for making a batch in larger container (no larger than 1 litre) in care settings, formula should be cooled in small containers where possible, as larger container may result in slower cooling rate.
PIF is not a sterile product and may be contaminated with pathogens that can cause serious illness. For high-risk infants who are not breastfed, caregivers are encouraged to use commercially sterile liquid formula, whenever possible and feasible.
Key Points to Note:
- PIF is not a sterile product and may be contaminated with pathogens that can cause serious illness.
- Neonates and infants less than two months of age, in particular pre-term infants, low-birth-weight infants and infants with weakened immunity, are at greatest risk for Enterobacter sakazakii infections.
- Microbiological hazards are controlled by appropriate risk reduction measures applied by both manufacturers of PIF and caregivers.
Advice to Caregivers
- Reconstitute PIF with water that is no less than 70℃ (water left for no more than 30 minutes after boiling) and minimise the time from preparation to consumption.
- Feeds prepared in advance should be cooled immediately after preparation and stored in a refrigerator. Reconstituted feed should be re-warmed immediately before feeding and used within 24 hours of preparation.
- Re-warm reconstituted feed for no more than 15 minutes by placing in a container of warm water with occasional shake or swirl; the level of the water should be below the top of the bottle.
- Wherever possible, commercially sterile ready-to-feed liquid formula should be used for infants at greater risk.
Advice to Manufacturers
- Implement preventive measures (such as Good Manufacturing Practice / Good Hygiene Practice and Hazard Analysis & Critical Control Point) as well as monitoring and environmental management programmes.
- Communicate the risk reduction measures that the caregiver should follow for the safe preparation, handling and use of powdered formula on product label.