Consumers often put a bout of food poisoning down to having eaten eggs or meat. But some cases of food poisoning are actually caused by eating raw vegetables, according to PhD researcher Eelco Franz, at the Organic Farming Systems Group. Bacteria that cause diarrhoea, like salmonella and E. coli 0157, come in contact with lettuce plants through manure and are even taken up by the plants.
The laboratory experiments showed that contamination is not only on the outside of the plant, however. The lettuce plants absorb the bacteria and can therefore also be internally infected. According to Franz, the concentration levels – up to a thousand bacteria cells per gram of lettuce – are high enough to make a person ill after eating contaminated lettuce. What’s more, internal contamination means that washing the lettuce has no effect.
A way to reduce the chance of contamination would be to compost manure. Another measure would be to ensure that there is a period of at least four months between the moment of manure production and harvesting the vegetables. Franz emphasises that there have been no known outbreaks of food poisoning through raw vegetables so far in the Netherlands. Nevertheless, he is sure that among people who have assumed they have had food poisoning as a result of eating egg or chicken sate, there will cases where fresh vegetables were the culprit.
The Food and Consumer Product Safety Authority (VWA) is taking the danger of infection through raw vegetables seriously and is looking into ways to prevent the presence of dangerous bacteria in vegetable and fruit products. VWA project leader Paul in ’t Veld: ‘We already knew that pathogenic bacteria are found on lettuce leaves. It’s news that they are also found in the leaves, but it doesn’t really surprise me. We will be doing screening to see how serious the problem is in vegetables on the market.’ He expects to be able to present the first results of the screening in two years. / GvM