justify concern that the incidence of foodborne disease is high and may be increasing.

At least five trends contribute to the possible increase in foodborne disease: changes in diet, the increasing use of commercial food services, new methods of producing and distributing food, new or re-emerging infectious foodborne agents, and the growing number of people at high risk for severe or fatal foodborne diseases.

Diet

Annual food expenditures in the United States, as a share of disposable personal income, decreased from 14 percent to 11 percent from 1970 to 1996 (Putnam and Allshouse, 1997). No industrialized nation spends a smaller share of its wealth on food than the United States. For much of the population, readily available food is more varied and more affordable than ever before. For example, in the 1960s, an average US grocery store had fewer than 7,000 food items available. Today, an average US grocery store sells about 30,000 food items (FMI, 1997b), and over 12,000 new products are introduced each year (New Product News, 1998).

During this time when relative costs of the US food supply are decreasing, per capita consumption of many foods has changed substantially. Public health efforts to promote a ''heart-healthy" diet have helped to boost the consumption of fresh fruits and vegetables. On a per capita basis, in 1995, Americans ate about 31 lb more commercially grown vegetables, including potatoes and sweet potatoes, and 24 lb more fresh fruit than in 1970 (Putnam and Allshouse, 1997). As the consumption and variety of produce have increased, so has the importation of produce from developing countries. The General Accounting Office estimates that in 1995 one-third of all fresh fruit consumed in the United States was imported (GAO, 1998). Food imports have increased both because of lower production costs in foreign countries and because of consumer demand for year-round supplies of fruits and vegetables that have limited growing seasons in the United States. For example, 17 percent of cantaloupes, 52 percent of green onions, 36 percent of cucumbers, and 34 percent of tomatoes sold in the United States in 1996 were grown in Mexico (Osterholm et al., 1998). Seasonally, as much as 79 percent of a particular commodity consumed in this country has been raised in Mexico alone, and the percentage of produce from other developing countries consumed here is growing rapidly. Fresh produce items were the leading vehicle associated with foodborne disease outbreaks in Minnesota from 1990 to 1996, accounting for almost one-third of all outbreaks (Osterholm et al., 1998). This percentage is higher than that available from national foodborne disease surveillance data and possibly reflects more active surveillance in that state.

Other trends in the United States are the decreasing consumption of beef and the increased consumption of chicken and seafood. In 1970, the average



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