Vegetables and Fruits as the Principle Vehicle for Norovirus, Bacteria and Parasites

26 Jul 2013 09.10 am by L.M.

Recent research on the sources of disease outbreaks suggest that fruits and vegetables play an important role in the transmission of food-borne illnesses that “were traditionally associated with foods of animal origin” said Professor Cedric N Berger from Imperial University London. In fact, contrary to popular belief, Professor Caroline Smith DeWaal, Director of the food safety program at the Centre for Science in the Public interest, found that in the U.S “produce outbreaks cause more illnesses on average than beef, poultry and seafood outbreaks”. The main causes for outbreaks of food-borne illness highlighted in her discussion are “green-based salads, berries, tomatoes, lettuce and sprouts”. 


What raises concern is that there is little evidence to support the comforting belief that as agricultural methods and practices advances, we become less at risk to food-borne illnesses. Instead, Berger finds that over the last few decades more people are getting sick! He states “the proportion of food-borne illnesses associated with raw produce increased from 1% in the 1970s to 12% in the 1990s”. While it could be argued that these increases are a result of an improvement in detecting food-borne illness, Berger argues otherwise. Their report clearly states that this increase is very likely to be associated with a “true increase in contamination”.


Both studies find that there are three main culprits causing food-borne illnesses - noroviruses, bacteria and parasites. “Norovirus is now widely viewed as the leading cause of food-borne illness” states Berger and accounts from anywhere between 40% to 60% of food borne illnesses. Noroviruses are most commonly found in green- based salads, lettuce and certain unspecified fruits, however in Europe it is, also associated with raspberries. Food that is contaminated with noroviruses are usually due to poor handling by individuals and the use of irrigation or washing water that has been contaminated with a norovirus. 


Bacterial pathogens are another major cause of food-borne illness. Between 1973-1997 bacteria was responsible for up to 60% of outbreaks. 30% of the outbreaks were caused by salmonella, bacteria that is often misunderstood to be found only on meat. Rather, salmonella can be found in sprouts, green salads, tomatoes, mushrooms, potatoes and melons. E. Coli was the second leading cause for bacteria related food borne outbreaks. E. Coli is found in green salads and lettuce. In the U.S, between 1973-1997 parasites accounted for 16% of food-borne illness of which Cyclospora was the most common parasite. 


As mentioned earlier, food-borne illness is becoming more and more common throughout the world. Both Berge’s and Dewaal’s findings are consistent with this belief. There are three general reasons that are said to cause this increase. Firstly, pressure on limited agricultural land has brought animal and crop production closer and this has caused contamination of crops through animal manure or the need to recycle water for irrigation. Secondly, products such as bagged salads and ready-to-eat vegetables which have been marketed to meet greater consumer demand for convenience and variety are also causing the increase in food-borne illness. Despite the claim ready-to-eat there have been a number of cases where noroviruses and bacteria have been found on pre-packaged vegetables. Thirdly, a growing global market and food trade over a greater geographical area has led to the rapid spread of contaminated foods.  If left poorly checked by the relevant authorities and regulatory bodies contaminated pre-packaged foods, raw produce and seeds can be easily transmitted to all corners of the world. 


The increase in food-borne illnesses has heightened efforts amongst food authorities around the world. Increased efforts are being made to manage and limit food-borne illnesses at the manufacturing, distributional and agricultural levels. It is however, unfortunate for individual consumers that there are limited precautions, which can be taken. Apart from parasites, it is very difficult to detect noroviruses or bacteria in the quantities that are enough to cause serious illness.  As an individual the best methods to guard against food-borne illnesses are to thoroughly assess the quality and safety of food and to always wash food before consumption. 


bacteria. virus  

  • Berger C N., Sodha R K., Griffin P M., Pink D, Hand P & Frankel G. (2010),’Fresh fruit and vegetables as vehicles for the transmission of human pathogens’, Environmental Microbiology, Vol.12:9, pp. 2385-2397.
  • DeWaal C S. & Bhuiya F 2005, OUTBREAKS BY THE NUMBERS: FRUITS AND VEGETABLES, Center For Science In The Public Interest Washington DC 20009, accessed at

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