Epidemiology Foodborne Disease

From 1988 to 1992, a total of 2423 outbreaks of foodborne diseases in the United States were reported to the CDC: 77,373 persons developed predominantly diarrheal illness.3 This number represents only a small fraction of foodborne outbreaks. Most infections are undiagnosed or unreported. It has been estimated that foodborne illness affects 6 to 80 million people in the United States and causes 9000 deaths each year. 4 On a global scale, the prevalence of all diarrheal illnesses has been estimated to be 3 to 5 billion cases per year and is associated with 5 to 10 million deaths per year or approximately 27,000 deaths per day. 5

The epidemiology of foodborne illnesses has evolved quickly over the past few decades in response to several influences. New pathogens such as Escherichia coli O157:H7,6 enteroinvasive Klebsiella pneumoniae,6 and Cyclospora cayetanensis7 have been recognized as recent causes of foodborne illness. The expanding role of pathogens such as Campylobacter jejuni, Listeria monocytogenes, and Yersinia enterocolitica, previously unrecognized causes of foodborne illness, has brought them to the forefront.7 A growing list of foods, previously thought to be safe, have been identified as new vehicles for transmission.

The evolution of foodborne epidemiology over the past few decades has been a reflection of changes in the food supply and population demographics. International trade has allowed people to come in contact with previously unfamiliar pathogens that are native to remote parts of the world. 4 Bacteria, viruses, parasites, and chemical contamination at the site of processing can be disseminated to a multitude of locations thousands of miles away. Low-dose contamination at a central processing site can cause widespread outbreaks that often are undetected.48 Consolidation of the food industry has led to a larger market share and greater geographic distribution of products from a single supplier or distributor. 4 This increases the risk of larger outbreaks of disease. In 1994, a nationwide outbreak of over 224,000 illnesses of Salmonella serotype Enteritidis from one distributor occurred when ice cream premix was transported in tanker trucks that had not been completely sanitized after transporting nonpasteurized liquid eggs. No source for contamination was found in the manufacturing plant. 9

The eating habits of the US population have changed, with a greater emphasis on incorporating fruits and vegetables in the diet. 1 To meet this increased demand, the volume of imported fresh fruits and vegetables has escalated. Imports can account for more than 75 percent of grocery-store fruit and vegetable stock. 1 Outbreaks of foodborne illness have occurred recently in produce such as fresh squeezed orange juice, raspberries, frozen strawberries, sliced tomatoes, and lettuce. 4

Population dietary patterns have changed as a larger percentage of meals are consumed outside the home. 4 Nearly 80 percent of foodborne outbreaks in the United States from 1988 to 1992 occurred in cafeterias, restaurants, or delicatessens.3 The number and array of food-service establishments that mass produce food has expanded. Many restaurants rely on transient personnel who have inadequate knowledge of food-handling techniques. 10 In the home, there has been a decline in basic food preparation skills. Many adults who prepare meals do not routinely wash their hands after handling raw meat or poultry. 10

The number and the percentage of people with increased vulnerability to illness have changed. The United States will continue to experience a demographic shift to an older population base: 20 percent of the population will be over age 65 by the year 2040. 11 Patients with compromised immunity secondary to AIDS, immunosuppressants, chemotherapy, or chronic illnesses also represent an expanding segment of the population with heightened susceptibility to foodborne illness.4,!1

Travelers are at an increased risk of foodborne illnesses secondary to exposure to new, previously unseen pathogens, increased exposure through meals at hotels and restaurants, and unpredictable standards for public health cleanliness and water-supply systems. 12 The relative risk of foodborne infection with viruses, bacteria, or parasites varies by country, but ranges from 20 to 50 percent for all travelers.1 Enterotoxigenic E. coli is recognized as the major cause of travelers' diarrhea,5 but other strains of E. coli are associated with travel, including enterohemorrhagic and enteroinvasive E. coli.12 The prevalence of Salmonella typhi necessitates typhoid immunization for travelers to many countries.12 Salmonella serotype Enteritidis outbreaks have occurred on airlines and railways from contaminated meals.12 Other pathogens associated with international travel include Brucella, hepatitis A,12 Vibrio, Shigella, Campylobacter, Giardia lamblia, and Cryptosporidium.5

Food-industry influences have contributed to the emergence of new pathogens in foodborne disease. The common use of antibiotics in animal food reservoirs and humans have facilitated an increase of antibiotic resistant strains of Salmonella and Campylobacter jejuni.4 The disposal of the more than 1 billion tons of manure and associated pathogens that are an annual by-product of the farm industry is a growing dilemma and can contribute to the contamination of fruits and vegetables at harvest.4

National and international surveillance of foodborne illness is subject to constraints that limit reliable information and lead to inaccurate estimates of the magnitude of the problem. Globally, it is estimated that only 1 to 10 percent of the true incidents of foodborne illnesses are reported. 13 Some countries have estimated that foodborne illnesses may be 300 to 350 times more frequent than reported.13

There are a variety of reasons for this worldwide underestimation of illness. Many countries have failed to implement even a basic foodborne-disease surveillance system. Cholera is the only foodborne disease that must be reported internationally.13 It is difficult to compare data from different countries because of the lack of uniform data collection. As well, many governments are reluctant to provide information on foodborne diseases, particularly if a country's economy is based on tourism or food exports.13 In the majority of countries, foodborne-illness surveillance infrastructures or laboratories are nonexistent or function with inadequate resources making these countries vulnerable to outbreaks or epidemics of foodborne disease. 13

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