The Sorrows of Salad

Having spent four months working on a paper on salads, food poisoning and public health, I heard of the publication of Joanna Blythman’s Swallow This on BBC Radio 4’s Food Programme the other week with a  mixture of anxiety and anticipation. I need not have worried: Blythman’s topic is the iniquities of the food industries, and what they put into processed and manipulated foods to improve their flavour, appearance, keeping qualities or cheapness. Salads of the pre-packed lettuce variety feature briefly, and bacteria get half a dozen or so honourable mentions, but none of them are specified, as in e.g. E. coli 0157: H7. Almost all Blythman’s references are to web-based sources, so my hours spent with the Journal of Food and Milk Technology, latterly the Journal of Food Protection, have not been in vain. My paper is rather about faecal contamination, environmental pollution, food hygiene in relation to growing conditions, production and processing methods, food handling practices, the ability of pathogenic micro-organisms from typhoid to norovirus to survive on and in raw fruit and vegetables, and the modern food revolution which has opened up a whole new genre of food poisoning incidents. In 2013 Hugh Pennington declared bagged salads to be more dangerous than hamburgers – and so they are. With the hamburger you have a form of self-defence: as long as it is properly cooked it is safe; with a salad vegetable, especially if eaten raw or lightly cooked, even if it come labelled as pre-washed and ready-to-eat, there is no safeguard option. In fact the fragility of some of these products, especially the herbs and baby leaves popular in pre-prepared salads, is such that they are not properly washed while the very procedures of slicing and mixing just increases their bacterial load.

The risks associated with eating salad vegetables have been known since the beginning of the twentieth century, but until the 1970s food poisoning outbreaks were very rarely linked to them.  That began to change in the 1970s, and there emerged, as the now Professor of Environmental Health Sciences, Minnesota University, Craig W. Hedberg, and his then colleagues at the state’s Department of Heath observed in 1994, an altered epidemiology of food-borne diseases in the United States. Before this meat products, milk, eggs and shellfish were the main foods linked to food poisoning. But when the link was made between saturated fat consumption, heart disease and cancer in the 1970s, successful health campaigns were launched to change the nation’s eating habits. In the US, consumption of fruit and vegetables rose by 16% and 29% respectively from 1970 through 1990; and whereas 12 fruit and vegetable associated food poisoning outbreaks were recorded in the US in the 1970s, in the 1980s that total reached 60 (and rose to 111 in the 1990s).  Moreover, where food poisoning outbreaks in the US had been largely associated with staphylococcal intoxication since c. 1940, a whole new spectrum of such infections had been identified since the mid-1970s, and large food-related outbreaks of hepatitis A, shigellosis and salmonellosis due to fruit and vegetables had been recorded.  Changes in diet were compounded by increasing use of commercial food stations, where salad bars were now a regular and popular feature, and, by the 1990s, by large and complex networks of food distribution with an increasingly international character.

Most of us give little thought to the procedures of food production from field to plate, at least where fruit and vegetables are concerned (meat has been more of a public issue). It has been known since the 1910s that bacteria of the Salmonella family can survive for weeks in faecally contaminated soil. And all soils are unavoidably contaminated by small rodents and wild birds, besides being vulnerable to more or less contamination by larger animals, manure, and human beings. Plants such as tomatoes may be infected by insects visiting their flowers, or by spray irrigation of their leaves and stems. Such contamination is not just surface, but penetrates the fruit tissue. As recently as 2012 it was noted that faecal contamination of the growing environment by wildlife can be an on-going source of contamination for field grown crops. Fruit pickers can also act as vehicles of infection as repeated outbreaks of hepatitis A associated with frozen raspberries have shown, and food outlet handlers from market stall to world class restaurants have a dodgy record of safety with norovirus. Many of these foodborne pathogens are very resilient, and there are a lot of them: some 2,000 plus Salmonella, hepatitis A, several dysenteries, norovirus, camplylobacter, cryptosporidium, E. coli 0157: H7, to name only the best known. Eaters beware: if you happen to strike unlucky it’s just as likely to be the salad, fruit or vegetable, as the burger.

Anne Hardy, Honorary Professor, Centre for History in Public Health (PHP)