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By Root 1141 0

on diarrheal symptoms, and the reporting system is voluntary, these figures almost certainly underestimate the extent of foodborne illness. A 1998 report on food safety from the Institute of Medicine (IOM) in Washington, DC, for example, gave a higher estimate. It assumed that adults in the United States average about 1.4 episodes of diarrhea every year, and that food is implicated in about one-quarter of those episodes; these assumptions yielded an estimate of 91 million cases per year.10 Some experts suspect that even this number may be too low. Such uncertainty means that reported trends in foodborne illness must be interpreted with caution. In 2002, FoodNet data suggested that cases of infection from four key pathogens had declined markedly since 1996, but cases caused by some strains of Salmonella had increased.11 Overall, the accuracy and significance of reported trends remain unclear.

If the extent of foodborne illness is uncertain, so must be estimates of its cost to society. Here are some examples of the wide range of figures reported from 1989 to 1998: $4.8 to $23 billion in 1989, $23 million to $6 billion in 1994, $5.6 to $9.4 billion in 1995, $12.9 billion (from illness caused by just six types of bacteria) in 1996, and $37.1 billion in 1998. Agricultural economists estimate that the costs of foodborne illness in children alone came to $2.3 billion in 2000.12 Whatever the correct figure might be, it surely underestimates the costs to the victims in pain and inconvenience; to taxpayers in medical treatment for the indigent, higher health insurance premiums, public health surveillance systems, and investigations of outbreaks (estimated at $200,000 each); and to the food industry in plant closings, cleanup, and recalls as well as in legal fees, claim settlements, and higher insurance premiums.8

Raising the Stakes: Food Sources and Virulence

Regardless of the accuracy of cost and case estimates, one trend is clear: an increasingly broad range of foods is contaminated with harmful bacteria. Back in the 1970s, outbreaks of foodborne illness were most often traced to improperly stored turkey stuffing and deviled eggs prepared by home cooks.13 Before examining how the food sources of contamination have expanded, we need to deal with one further complication: the distinction between cases and outbreaks. Cases refers to the number of individuals who become ill—whether or not they report the disease. In contrast, outbreaks always are reported; authorities discover them when more than one person gets sick from the same food source and doctors report the illnesses to health officials. It is easier to identify cases—and, therefore, report them—when an illness occurs right after the food is eaten. Cases that occur with a delay in onset are more difficult to attribute to specific foods and are much more likely to go unreported, even when they affect much larger numbers of people.

With these distinctions in mind, the tracking information indicates a change in the food sources of outbreaks: seafood ranks first, followed by eggs, fruits and vegetables (sprouts, lettuce, berries, cantaloupe), beef, poultry, and foods such as salads and sandwiches made with multiple ingredients. In part because so many more meals are consumed outside the home, foods other than those prepared by home cooks now account for 80% of the outbreaks (although not necessarily 80% of the cases of food-borne illness).14

The outbreaks have changed in one additional respect: they are getting nastier. Most used to be due to relatively benign species of Salmonella, Staphylococcus, Clostridium, Shigella, and Vibrio, but the more pathogenic strains observed since the 1990s are quite unforgiving. Among outbreaks of illness caused by Listeria monocytogenes, a particularly virulent species of bacteria, the death rate is 20% (table 3). For example, some years ago a carefully investigated Listeria outbreak among 142 people who had eaten a commercially produced unpasteurized soft cheese caused 48 deaths (of which 30 were fetuses or newborn children) and 13 cases of