1. What is Enterobacter sakazakii? What diseases can the bacteria cause?
Enterobacter sakazakii is a bacterium belonging to the family
Enterobacteriaceae, which contains a number of bacterial species found in
the human and animal gut and the environment. The microorganism has been
implicated in outbreaks causing meningitis or enteritis, especially in
infants. In the few outbreaks reported 20% to >50% of the infants who
contracted the disease died. For survivors, severe lasting complications can
result including neurological disorders. The outcome related to adult
disease seems to be significantly milder.
2. Where does the bacterium come from? Does it also exist in the human gut?
The natural habitat of Enterobacter sakazakii is not well understood. The
bacterium can be detected in the gut of healthy humans, most probably as an
intermittent guest. It can also be found in the gut of animals as well as in
3. How does infant formula get contaminated with Enterobacter sakazakii? Can
other foods also be contaminated?
Basically there are three routes by which Enterobacter sakazakii can enter
a) through the raw material used for producing the formula;
b) through contamination of the formula or other dry ingredients after
c) through contamination of the formula as it is being reconstituted by the
caregiver just prior to feeding.
Enterobacter sakazakii has been detected in other types of food, but only
powdered infant formula has been linked to outbreaks of disease.
4. Which are the main groups at risk?
Enterobacter sakazakii has caused disease in all age groups. From the age
distribution of reported cases it is deduced that infants (children less
than 1 year old) are at particular risk. Among infants those at greatest
risk for Enterobacter sakazakii infection are neonates (first 28 days),
particularly pre-term infants, low birth weight infants or immunocompromised
infants. Infants of HIV-positive mothers are also at risk both because they
may specifically require infant formula and may be more susceptible to
infection. This, and low birth weight, may be of particular concern for some
developing countries, where the proportion of such infants is higher than in
developed countries (see also Q10).
5. How can this risk be minimized/reduced?
The recent expert meeting recommended that caregivers to infants,
particularly those at high risk (see Q 4.), should be regularly alerted to
the fact that powdered infant formula is not a sterile product.
In situations where the mother cannot breastfeed, or chooses not to
breastfeed for any reason, caregivers should use, whenever possible and
feasible, commercially sterile liquid formula or include a decontamination
step in the preparation of powdered infant formula (such as reconstituting
with boiling water or heating reconstituted formula)2.
A preliminary risk assessment further indicated that reduced holding (time
between rehydration of the formula and consumption) and feeding times for
the reconstituted formula decrease the risk of infecting infants. A
combination of control measures would have the greatest impact on reducing
With current technology it seems not to be possible to produce sterile
powdered infant formula. However, recommendations are being made to the
industry on how they can improve the safety of powdered infant formula.
6. Are there international standards for maximum levels of the bacterium?
What level of safety do these standards ensure?
The FAO/WHO Codex Alimentarius Commission sets international standards for
food. Current Codex microbiological specifications for powdered infant
formula limit the amount of bacteria called coliforms, which includes
Enterobacter sakazakii. While this limit probably helps to prevent a number
of outbreaks, it does not confer a sufficient level of safety as evidenced
by outbreaks caused by powdered formula meeting the current specifications.
Given new information on this emerging problem, the recent expert meeting
recommended that Codex revise the international standard to better address
the microbiological risks of powdered infant formula, including establishing
a microbial specification for Enterobacter sakazakii.
7. Are there differences in the levels of Enterobacter sakazakii in infant
formula depending on the producer?
At the moment we do not have any data that would demonstrate any difference
between the infant formulas of different producers.
8. Is the risk similar in all regions and countries?
There have been reported cases of Enterobacter sakazakii infections due to
contaminated infant formula in only a few developed countries. It is likely
that there is a significant underreporting of infections in all countries.
The absence of reports is probably due to a lack of awareness of the problem
rather than an absence of illness. In general, the limitations of current
surveillance systems in most countries would add to the explanation for the
lack of reported cases. Since infant formula is widely used, the presence of
Enterobacter sakazakii in infant formula and its potential effects in
infants could well be a significant public health problem in most countries.
1 The UN guidance for these infant is that where replacement feeding is
acceptable, feasible, affordable, sustainable and safe, avoidance of all
breastfeeding is recommended, and powdered infant formula may be an option.
Some of these infant maybe HIV-positive and thus immunocompromised.
2 Nutritional and other factors need to be considered, e.g. alteration of
nutritional content, risk from burns due to handling boiling or hot
water/formula. The formula should thereafter be cooled and handled
9. Could there be other bacteria in infant formula that could cause
problems, or is it only the Enterobacter sakazakii?
The current Codex standards do not allow pathogens such as Salmonella, in
powdered infant formula. The current Codex microbiological specification for
Salmonella is the absence of Salmonella in 60 samples of 25 grams each.
However, there have been reported outbreaks associated with Salmonella in
powdered infant formula.
10. Would these risks be avoided if an infant were breastfed instead of fed
on infant formula?
In the current state of knowledge, no exclusively breastfed infants have
been reported to have Enterobacter sakazakii infections. Based on the
available information, in 50-80 % of cases, powdered infant formula is both
the vehicle and the source (direct or indirect) of E. sakazakiiinduced
illness. Breastfeeding is beneficial to infants in all instances. The WHO
recommendation is that, on a population basis, infants should be exclusively
breastfed for the first six months of life and that breastfeeding continue
together with complementary feeding until the age of two years or beyond.
There is ample evidence that infants who are partially or not breastfed are
at significantly higher risk of morbidity and mortality due to diarrhoeal
Please also refer to Question 4 above, there are situations where the mother
cannot breastfeed or chooses not to breastfeed.
11. What is being done to remedy this problem?
Since FAO and WHO first became aware of the issue, the two organizations
have, together with Member countries, been working to gather data and
expertise relevant to addressing this issue. This work started in 2003 and
there is now good evidence on which to move forward. The FAO/WHO expert
meeting, February 2004, in Geneva, examined what is known about production
methods, risk factors, disease incidence, etc. and have now issued a set of
recommendations to advise FAO/WHO, Codex and Member countries on relevant
options to manage and avoid this risk (see Q5). A summary report of this
meeting is available.
12. What is the magnitude of the problem?
The true magnitude of the problem is unknown due to lack of surveillance and
reporting systems for Enterobacter sakazakii in most countries.
The magnitude of the problem is generally described in terms of frequency
and severity. The frequency of the disease in infants appears to be very
low, yet the disease is devastating.
A review of cases in infants reported in the English literature from 1961 to
2003 found 48 cases of Enterobacter sakazakii induced illness among infants.
The US FoodNet 2002 survey found that the rate of invasive Enterobacter
sakazakii infection among infants under one years old was 1 per 100 000.
Mortality rates from Enterobacter sakazakii infection have been reported to
be from 20% to >50%. Significant long-term effects in the form of
neurological deficiencies can result from the infection, especially among
those with severe meningitis and cerebritis.
* taken from WHO