Largescale food production and distribution

In 1900, 39 percent of the US population lived and worked on family farms of less than a few hundred acres. Food animals were raised in small herds or groups, and slaughtered locally. Due to the lack of refrigeration, meat, milk, and eggs were transported only a few miles from their origin, and then consumed locally and relatively quickly. Fresh produce was limited to what was in season. Overall, food production was done manually and was labor intensive. Mechanization increased productivity and promoted competition. Farms became larger in size, requiring more capital investment, and today less than 2 percent of the population lives and works on US farms (see Table 8.3). Food animals now are raised commercially in very large herds or flocks under conditions to maximize weight gain in short grow-out periods. Meat, milk, and eggs are shipped considerable distances and, due to refrigeration, are consumed later after harvest. Importation of produce and other crops has brought an end to seasonality, with many fresh items now available year round. Farming in the US is now agribusiness, characterized by more intensive land use rather than development of new farmland, commercial rather than family ownership, and a vertically integrated organizational structure. These trends have had considerable ramifications on the safety of the food supply.

Table 8.3 Selected trends in US agriculture



US population living on farms



No. of farms (millions)



Average farm size (acres)



Mechanization (wheel tractors)



Government payments


$5 billion

Farms growing or raising:

• Cattle



• Milk cows



• Chickens



• Corn



• Vegetables



• Soybeans



Data from Economic Research Service, United States Department of Agriculture.

Data from Economic Research Service, United States Department of Agriculture.

Mass production and distribution of foods permit economies of scale in production, processing, and retailing, but provide an Achilles heel should a contamination event occur. Outbreaks of food-borne illness in recent years have occurred on a size and scale not seen 50 years ago. The classic example of the old outbreak was that of staphylococcal food-poisoning at the church picnic, with a short incubation period, rapid recognition, and affecting less than 50 persons in a circumscribed group. Examples of very large outbreaks today include the thousands of cases of salmonella infections from contaminated ice cream (Hennessy et al., 1996) and milk (Ryan et al., 1987); E. coli O157:H7 infections from hamburger (Bell et al., 1994), as well as radish sprouts in Japan (Michino et al., 1999); and hepatitis A from green onions (Wheeler et al., 2005). Each of these outbreaks occurred across multiple states or prefectures and population groups. The scale of these food-borne outbreaks was due to centralized production and distribution, and is akin to that of urban water-borne outbreaks before municipal chlorination.

Food distribution networks are now quite complex, as well as covering widespread geographic regions (Hedberg et al., 1994). Both finished products and ingredients may be shipped substantial distances, passing through brokers, distributors, and other middle suppliers to food processors and retailers. Products and ingredients may be commingled with that from other sources, so that even product from a small producer can contaminate large lots - for example, contaminated mozzarella cheese from one small producer was supplied to four larger processors who shredded it into larger batches, resulting in a multi-state outbreak of salmonellosis (Hedberg et al., 1992). One hamburger patty can represent meat from 600 individual cattle. These aspects impact outbreak recognition, particularly when sporadic or low-level contamination of product occurs, since the attack rate is usually low and cases are geographically dispersed, and outbreak control efforts may be thwarted by the inability to trace product back ultimately to the source.

Aquaculture as a food production sector did not exist a century ago but is growing rapidly worldwide, partly as a response to produce foods of high protein value for an expanding global population. By 2030, aquaculture farms, both marine and freshwater, will produce half of fish consumption globally (Tidwell and Alan, 2001). Although food-borne trematodiasis is an emerging disease mainly seen in the developing world (Keiser and Utzinger, 2005), international markets and trade are simply the conduit for these pathogens to non-travelers in industrialized countries. Paragonimus infections were recently noted in several Californians who had eaten raw imported crab (ProMed, 2006).

Antimicrobial drug resistance has increased among bacterial food-borne pathogens, with increased severity and increased mortality seen in human infections with drug-resistant compared with drug-susceptible strains (Molbak, 2005). Agricultural use of antibiotics for both therapeutic and non-therapeutic purposes in food animals is widely regarded as the main selection pressure for drug resistant strains. Transfer of drug-resistant pathogens to humans via the food chain has been documented (Spika et al., 1987), and several lines of evidence support the linkage of agricultural use of antibiotics and human illness with drug-resistant bacterial pathogens (reviewed in Swartz, 2002). Agricultural use of antibiotics, particularly for non-therapeutic purposes (growth promotion), dwarfs human use. The topic of agricultural use of antibiotics is discussed in Chapter 9.

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