Foodborne Illness Trends in the United States
Kristyn Howe, Lauren Howe and Paul Ebner
Foodborne illnesses are caused by a variety of different microorganisms. Many of these pathogens, such as Salmonella, are regularly found in the intestinal tract of livestock. Others, such as Clostridium, also are found in soil and marine environments. Foodborne illnesses can occur when these organisms find their way to foods, and those foods are then improperly handled or prepared. Over the past two decades, the incidence and prevalence of foodborne diseases caused by different pathogens has varied, as have the most common food sources. Reasons for these variations include everything from differences in our ability to detect and identify pathogens to differences in consumption levels of specific foods. The aim of this fact sheet is to report the major trends in foodborne illnesses over the past 20 years in the United States, observing changes in how theses illnesses are transmitted and describing why these changes have occurred.
Major Pathogens and Their Carriers
Salmonella is the leading cause of bacterial foodborne illness. It is a ubiquitous organism and can be found on meat, dairy products, produce, and even processed foods such as peanut butter. These foods usually become contaminated upon direct or indirect contact with Salmonella-containing animal or human feces. Symptoms of a Salmonella infection (salmonellosis) include fever, vomiting, stomach cramps and diarrhea. Most cases of salmonellosis are self-limiting and last 2-5 days. Infections with Salmonella typhi (typhoid fever), a type of Salmonella found only in humans, are much more serious. Typhoid fever can last up to six weeks with sustained fevers as high as 104 degrees Fahrenheit, and can be fatal in some cases. The Centers for Disease Control and Prevention estimate that there are more than 100 outbreaks of salmonellosis in the United States each year, resulting in approximately 40,000 reported illnesses. This figure increased from 1996-2000 but has remained at relatively constant levels since (Figure 1). One reason for this increase is the identification of Salmonella in foods not typically associated with the organism. Salmonella has been found on fresh, low-processed foods for decades, but in the past 10 years it has been increasingly identified in processed foods as well. For example, peanut butter was considered a low-risk food until a Salmonella outbreak linked to a peanut butter facility in 2007. The peanut butter-associated outbreak resulted in the recall of every food product suspected to contain the peanut butter, from crackers to granola bars to dog biscuits.
Clostridium infections can be divided into two main categories: those caused by Clostridium perfringens and those caused by Clostridium botulinum. Clostridium perfringens infections result from consumption of foods that have not been cooked at proper temperatures. Foods most often associated with Clostridium perfringens include meats, gravy, soups and dairy products. In the past decade, the number of foodborne illness outbreaks associated with Clostridium perfringens has decreased significantly (Fig. 1). Clostridium botulinum infections (botulism) are primarily caused by consumption of improperly canned foods and honey. These infections are much rarer compared to other clostridial infections (~145 cases per year), but can lead to paralysis, visual impairments, lack of muscle coordination, difficulty breathing and, in some cases, death.
Consumption of foods contaminated with Staphylococcus also can result in illness. Foods potentially contaminated with Staphylococcus include meat and meat products, poultry and egg products, sandwich fillings, dairy products and salads such as egg, tuna, and potato. Staphylococcus releases a toxin in the body, which causes nausea, vomiting, cramping and, in severe cases, shock. Like Clostridium perfringens, Staphylococcus-associated foodborne illness outbreaks have decreased significantly since 2002 (Fig. 1).
The CDC estimate that there are approximately 265,000 cases of E. coli-associated foodborne illnesses each year in the United States. Infections have been associated with numerous foods, including unpasteurized juices, raw milk, unwashed produce and meats cooked below proper temperatures. E. coli infection symptoms include stomach cramps, diarrhea and vomiting. Serious infections can lead to renal failure and even death. A particularly dangerous type of E. coli -- E. coli O157:H7 -- has long been associated with ground beef.
Campylobacter infections are caused by the consumption of untreated water, unpasteurized milk, raw or undercooked meat or poultry, or other foods that have come into contact with feces of infected animals. Campylobacter infections (campylobacteriosis) are the second most frequent bacterial foodborne illness with approximately 35,000 culture-confirmed cases per year, with the number of unreported cases estimated to be much higher. Campylobacter infections cause symptoms similar to those of E. coli infections, with the possibility of developing into meningitis, urinary tract infections and Guillain-Barre syndrome (a rare form of paralysis). Outbreak numbers have increased somewhat since 1999 (Fig. 1). This trend has coincided with an increase in poultry and egg consumption in the U.S. (Fig. 3).
Listeria affects approximately 1,600 people per year. It is present in water, mud, silage, animal intestines and food processing environments. Infections cause flu-like symptoms, which can develop into more serious complications, including convulsions, confusion, coma and death. Listeria poses a serious threat to pregnant women, since the infection can spread from the mother to the unborn fetus. While the number of outbreaks of listeriosis each year in the United States is relatively low, the number of fatalities within an outbreak can be very high.
Norovirus infection is the most common foodborne illness caused by a virus. It is commonly referred to as “stomach flu,” although it is not related to the influenza virus. Like most foodborne illnesses, norovirus infections are frequently not reported, although it is estimated that up to 21 million cases occur each year. Infections are caused by contact with contaminated surfaces or people, consumption of foods that came in contact with contaminated surfaces, or consumption of uncooked shellfish harvested from contaminated water. Norovirus outbreaks are usually much larger than other foodborne disease outbreaks, since the disease is very easily transmitted from human-to-human.
Figure 1. Bacterial Foodborne Disease Outbreak Trends 1990-2008. Data were collected from the Centers for Disease Control and Prevention OutbreakNet Database.
Paul Ebner, PhD
Dept. of Animal Sciences