The E. coli outbreak: The source of infection may be food

So far, a source of the E. coli O157 bacteria which has caused a recent national disease outbreak has not been found. Investigation into the outbreak is led by the Norwegian Institute of Public Health. Experience has shown that food is an important source for this type of infection. Nofima Mat is assisting the food industry with our know-how in order to ensure safe food production and safe food for consumers.

Contact person
Portrettbilde av Even Heir
Contact person
Portrettbilde av Helga Næs
Helga Næs

Research Director

Contact person
Portrettbilde av Lars Axelsson
Lars Axelsson

Senior Research Scientist
Phone: +47 901 57 584

We are involved in several projects contributing to safer food production and better handling of food in consumers’ homes. Good production and food handling routines are important to reduce risks connected with food infections. Read more about the bacteria here. Remember that even though food is often the source of infection for such outbreaks, other possible sources cannot be excluded.

What is enterohemorrhagic E. coli?

E. coli is a large group of bacteria which occur naturally in the gut flora of humans and animals. Most of these do not cause illness in humans as long as they remain in the gut, but in a few special cases they have the ability to cause illness. One subgroup of E. coli is shiga-toxin producing E. coli (STEC) or verotoxin producing E. coli (VTEC), which are synonymous. Some of the E. coli bacteria in this group may cause very serious diseases such as bloody diarrhoea or kidney failure, which may in some cases be fatal. This group is called enterohemorrhagic E. coli (EHEC). Children are at greater risk for illness than adults. The reason for this is not known, but is probably due to immunological causes. The number of bacteria needed in order to produce disease is usually quite low.

E. coli O157

The best known variant of EHEC is E. coli O157:H7, which previously was often known as the "hamburger bacteria" after it has led to several serious outbreaks in the USA since the 80s, where the source has been infected (and probably under cooked) hamburgers. The current tendency is that other variants than O157:H7 are detected as the cause of EHEC infections. This occurred in Norway in 2006 where there was an outbreak with E. coli O103 as the cause, and now again with the current outbreak where an atypical variant of E. coli O157 is the cause.

Several potential sources of infection

Ruminants, in particular, have been shown to be potential healthy disease carriers of EHEC bacteria. Cattle are often considered the main reservoir. It appears that the bacteria can occur in several hosts and can be more widespread than was thought previously. Food is an important source of infection, but infection can also be transferred through contaminated water, direct contact with animals and from person to person. Hand hygiene is an important preventive measure.

Food as a source of infection

Food that is not heat treated or which is insufficiently heat treated before consumption is a potential source of infection. Beef and particularly minced beef is considered a risk product. In such products, bacteria are as likely to be found within the product as on its surface. Large scale production and distribution can spread infection most effectively, if contaminated raw ingredients are used. Sufficient heat treatment will kill E. coli. Internationally, STEC has been determined in a number of food products, including meat, cured meat, fruit, vegetables, fish and shellfish. Transfer of bacteria to various food products can occur through cross contamination. This may occur during production, for instance during slaughtering or by the use of contaminated water for irrigating vegetables.

Poor kitchen hygiene can also be the cause of cross contamination between foods. Kitchen hygiene is important in order to reduce infection risk.

Food safety and quality  

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