Food Poisoning: The Real Extent of Foodborne Disease

Foodborne diseases affect about 48 million Americans each year, resulting in 128,000 hospitalizations and 3000 deaths, according to the latest estimates from the CDC.^1,2 Recent outbreaks of food poisoning include:

•Salmonellosis. In 2011, an outbreak of Salmonella enteritidis infection affected a total of 68 people who had eaten at a Mexican-style fast food restaurant chain, primarily in Texas and Oklahoma. Thirty-one percent of those who became ill were hospitalized. In 2012, an outbreak of human Salmonella infantis infection, which involved 22 people in the United States and Canada, was linked to contaminated dry dog food.

•Escherichia coli infection. In 2012, 29 people from 11 states who had eaten raw clover sprouts at a chain restaurant were infected with Shiga toxin–producing E coli O26.

•Listeriosis. In one of the more notorious outbreaks in the United States in recent years, 146 cases of Listeria monocytogenes infection were associated with contaminated cantaloupe in 2011. Thirty deaths were reported. In addition, one woman who was pregnant at the time of her illness had a miscarriage.

INCIDENCE

Although widespread or particularly virulent outbreaks of food poisoning attract public attention, the latest data from the CDC show that the incidence of foodborne disease may have actually decreased in recent years.^1,2 These new estimates are lower than those in the CDC’s previous report on the incidence of food-related illness in the United States, which was published in 1999.³ The difference largely results from improvements in the quality and quantity of the data and new methods used to estimate foodborne disease. For example, it is now known that most cases of norovirus infections are not spread by foodborne transmission, which has reduced the estimate of foodborne norovirus infection from 9.2 million to approximately 5.5 million cases per year. Because of data and method improvements, the 1999 and current estimates cannot be directly compared.

The CDC’s FoodNet surveillance system, which tracks trends among common foodborne pathogens, has documented a decrease of 20% in illnesses from key pathogens during the past 10 years. Among the proposed reasons for the decline in foodborne infections are the following:

•Enhanced knowledge about preventing contamination. PulseNet, the national molecular subtyping network for foodborne bacterial pathogens, can detect widely dispersed outbreaks and has greatly improved the detection and investigation of multistate outbreaks.

•Cleaner slaughter methods, microbial testing, and better inspections in ground beef processing plants.

•Regulatory agency prohibition of contamination of ground beef with E coli O157 (resulting in 234 beef recalls since E coli O157 was declared an adulterant in ground beef in 1994).

•Improvements in the FDA model Food Code.

•Increased awareness in food service establishments and consumers’ homes of the risk of consumption of undercooked ground beef.

THE CULPRIT PATHOGENS

Of the total estimate of 48 million illnesses annually, CDC estimates that 9.4 million illnesses are caused by 31 known foodborne pathogens. The top five pathogens that cause foodborne illness are listed in Table 1. The remaining 38 million illnesses result from unspecified agents, which include known agents without enough data to make specific estimates, agents not yet recognized as causing foodborne illness, and agents not yet discovered. In both the 1999 and current estimates, unspecified agents were responsible for roughly 80% of estimated illnesses.

Salmonella (Figure) was the leading cause of estimated hospitalizations and deaths (Tables 2 and 3); it was responsible for about 28% of deaths and 35% of hospitalizations due to known pathogens transmitted by food. About 90% of estimated illnesses, hospitalizations, and deaths were caused by seven pathogens: Salmonella, norovirus, Campylobacter, Toxoplasma, Shiga toxin–producing E coli O157, Listeria, and Clostridium perfringens. Norovirus was responsible for nearly 60% of estimated illnesses, but a much smaller proportion of severe disease.

Although infection with E coli O157 has decreased significantly, Salmonella and Vibrio infections have increased in recent years. Reducing Salmonella infection is difficult because it can contaminate a wide range of foods, including poultry, eggs, meat, fruits, vegetables, and even processed foods such as peanut butter. Vibrio infections are rare, but often serious, and are caused by consumption of contaminated seafood or exposure of an open wound to seawater.

CONTRIBUTING FACTORS

Among the factors that can contribute to foodborne disease are diet, food industry practices, and susceptibility.

Diet. Consumption of fresh fruits and vegetables has increased more than 50% since 1970.³ These foods may become contaminated at any time during growth, harvest, and distribution.

Moreover, it is difficult to monitor minimally processed foods such as fresh produce (ie, for practical purposes, it is nearly impossible to know whether apples that are shipped to processing plants for production of juice or cider were collected before or after they fell to the ground). During the past 10 years, alfalfa and clover sprouts, apples (unpasteurized juice or cider), basil, cantaloupe, green onions, lettuce, orange juice, raspberries, strawberries, and tomatoes have all been implicated in outbreaks of food poisoning.

Unpasteurized (“raw”) milk consumption has been linked to a number of outbreaks of foodborne illness. The rate of outbreaks caused by unpasteurized milk and products made from it, including cheese and yogurt, was 150 times greater than the rate of outbreaks linked to pasteurized milk, according to a study by the CDC.⁴ The 13-year review also revealed that the states where the sale of raw milk was legal had more than twice the rate of outbreaks as states where it was illegal.

The study included 121 dairy-related disease outbreaks, which caused 4413 illnesses, 239 hospitalizations and 3 deaths. In 60% of the outbreaks, state health officials determined raw milk products were the cause. Most of the hospitalizations (200 of 239) were in those who became ill after consumption of raw milk products. The study also found that the raw milk outbreaks disproportionately affected children and adolescents.

The well-established tendency for Americans to eat meals outside the home also contributes to the risk of foodborne disease. Most of the outbreaks during the past decade involved food consumption in restaurants and other sites outside the home.

Of course, such outbreaks are easier to identify and consequently are more frequently reported than food poisoning that occurs at home. However, the proliferation of fast-food restaurants, salad bars, and buffets increases the risk that unsafe food handling or preparation may cause widespread outbreaks.

Changes in the food industry. The internationalization of the food market has also exposed US consumers to new sources of infection. Foodborne disease outbreaks caused by imported food appeared to rise in 2009 and 2010, according to the CDC.⁵

From 2005 to 2010 in the United States, 39 outbreaks and 2348 illnesses were linked to imported food from 15 countries. Of those outbreaks, nearly half (17) occurred in 2009 and 2010. Overall, fish (17 outbreaks) was the most common source of implicated imported foodborne disease outbreaks, followed by spices (six outbreaks, including five from fresh or dried peppers). Nearly 45% of the imported foods causing outbreaks came from Asia.

According to a report by the Department of Agriculture’s Economic Research Service (ERS), US food imports grew from $41 billion in 1998 to $78 billion in 2007.⁶ Much of that growth has occurred in fruit and vegetables, seafood, and processed food products. The report estimated that as much as 85% of the seafood eaten in the United States is imported, and depending on the time of year, up to 60% of fresh produce is imported. Overall, about 16% of all food consumed in the United States is imported.

Susceptibility. The rising number of older adults in the United States may contribute to an increased incidence of foodborne disease. Most of those who became ill during the listeriosis outbreak associated with contaminated cantaloupe in 2011 were older than age 60 (median age, 77).⁷ Elderly persons are more susceptible to disease because of age-related changes in the gastrointestinal tract (ie, reduced production of gastric acid), a decrease in cellular immunity, and excessive use of antibiotics. Salmonella infection is the leading cause of death in nursing homes; deaths from foodborne Campylobacter species, Clostridium perfrigens, Staphylococcus aureus, and E coli O157 are also more likely to occur among nursing home residents than among persons in the general population.⁸

Immunocompromised persons are more susceptible to the pathogens that cause foodborne disease. This population includes transplant recipients, persons with AIDS and other immunosuppressive conditions, and those receiving corticosteroid and other immunosuppressant therapies.⁹

Infants, young children, and pregnant women are also at increased risk. For example, among women of reproductive age (15 to 44 years), the reported rate of listeriosis was markedly higher in pregnant women than in nonpregnant women.¹⁰

PREVENTION

Preventive measures to minimize the risk of foodborne disease fall into three main categories: precautionary steps for food handlers and consumers, hazard analysis critical control points (HACCPs) processes, and irradiation.

Precautionary steps.These include practical food handling measures, such as thorough heating of potentially hazardous foods, separating cooked and raw foods, and minimizing the risk of cross-contamination by washing hands, cutting boards, and other surfaces that come into contact with food. Consumers can reduce their risk of foodborne disease by avoiding high-risk items, such as runny eggs and raw shellfish.

HACCPs. Critical control point measures focus on identifying points in the food production process where contamination is most likely to occur and taking measures to reduce or eliminate hazards at these points. HACCP programs are found mainly in the meat, poultry, and seafood industries, where they are carried out by the processors and regulated by state or federal agencies.

Irradiation. Irradiation as a means to minimize the risk of foodborne disease has been gaining support from a wide variety of US and international organizations, including the CDC, the American Medical Association, and the World Health Organization. Although irradiation has been used effectively in meat, poultry, grains, and produce, not all foods can be irradiated without changing their quality. For example, meat with a high fat content may develop unpleasant tastes and odors; the whites of eggs may become milky and liquid; and alfalfa seeds do not seem to sprout as well if they are irradiated.¹¹