Tracking and Reporting Foodborne Disease Outbreaks

Eating or drinking a contaminated food or beverage can cause a foodborne illness. A foodborne disease outbreak occurs when two or more people get the same illness from the same contaminated food or drink.

Every year, about 48 million of us, roughly one in six people in the United States, get sick from eating contaminated food—it could be you, your spouse, your kids, your parents, or other loved ones. While most foodborne illnesses are not part of a recognized outbreak, outbreaks provide important information on how germs spread, which foods cause illness, and, how to prevent infection.

Size of Foodborne Disease Outbreaks

An outbreak’s size varies based on the pathogen, toxin, or chemical that caused it, the amount of contaminated food, point of contamination, serving location for the food, and number of people who ate it. Some examples:

• Local outbreak—A contaminated casserole served at a community supper may cause an outbreak among residents who know each other.
• Statewide or regional outbreak—A contaminated batch of ground beef sold at several locations of a grocery store chain may lead to illnesses in several counties.
• Nationwide outbreak—Contaminated produce from one farm may be shipped to grocery stores nationwide and sicken hundreds of people in many states. These are called multistate outbreaks.

Reports of Foodborne Disease Outbreaks

CDC has a long history of summarizing outbreak reports from local and state health departments. Data reported for each outbreak include the number of illnesses, hospitalizations, and deaths; the pathogens, toxins, and chemical agents that caused illnesses; the implicated food; the settings of food preparation and consumption; and factors contributing to food contamination.

CDC’s Foodborne Disease Outbreak Surveillance System gathers data on foodborne disease outbreaks from state, local, territorial, and tribal health departments. See reports summarizing the data.

Data on Foodborne Disease Outbreaks during 2009-2010

During January 1, 2009 through December 31, 2010, public health departments reported 1,527 foodborne disease outbreaks, resulting in 29,444 cases of illness, 1,184 hospitalizations, and 23 deaths.

• Among the 790 outbreaks with a laboratory-confirmed illness, norovirus was the most commonly reported infection, accounting for 42% of outbreaks; followed by Salmonella, with 30% of outbreaks.
• Of the 29,444 outbreak-related illnesses, 1,184 (4%) resulted in hospitalization. Salmonella caused the most outbreak-related hospitalizations (49%), followed by Shiga toxin-producing E. coli (16%), and norovirus (9%).
• Outbreaks caused by some pathogens were particularly severe. For example, Listeria outbreaks resulted in the highest proportion of persons hospitalized (82%), followed by Clostridium botulinum (67%), and paralytic shellfish poisoning (67%).
• Among the 23 deaths, 22 were linked to bacteria (9 Listeria, 5 Salmonella, E. coli O157, 3 Clostridium perfringens, and 1 Shigella), and 1 was linked to norovirus.

Identifying Common Foods and Germs

The pathogen-commodity pairs (germs and foods) responsible for the most outbreak-related illnesses, hospitalizations, and death in 2009-2010 were:

• Illnesses
  • Salmonella in eggs (2231 illnesses)
  • Salmonella in sprouts (493 illnesses)
  • Salmonella in vine-stalk vegetables (422 illnesses)
• Hospitalizations
  • Salmonella in vine-stalk vegetables (88 hospitalizations)
  • E. coli O157 in beef (46 hospitalizations)
  • Salmonella in sprouts (41 hospitalizations)
• Deaths
  • E. coli O157 in beef (3 deaths)
  • Salmonella in pork (2 deaths)
  • Listeria in dairy (2 deaths)

A large outbreak of Salmonella infections in 2010 caused nearly 2000 illnesses. Among the outbreaks attributed to a food vehicle composed of ingredients from only one of 17 defined food commodities, the commodities most often implicated were beef (13%), dairy (12%, nearly all unpasteurized), fish (12%), and poultry (11%).

Mishandling at Multiple Points

Mishandling at multiple points along the food production chain is sometimes at the root of an outbreak. After a food is contaminated, further mishandling, such as by undercooking or leaving it out for too long at an unsafe temperature, can result in an outbreak. Many pathogens grow to high numbers in just a few hours at room temperature.

Many Outbreaks Occur in Restaurants and at Home.
From 2009-2010, among the outbreaks with a known single setting where food was consumed, 48% were caused by food consumed in a restaurant or deli and 21% by food consumed in a private home.

CDC's Role in Foodborne Disease Outbreaks

State and local public health authorities investigate all foodborne disease outbreaks. CDC coordinates those that involve multiple states; such outbreaks usually result from contaminated food that is widely distributed to many states.

• Thirty-eight multistate outbreaks were reported (16 in 2009; 22 in 2010). Twenty-one were caused by Salmonella, 15 by Shiga toxin-producing E. coli (thirteen O157, one O145, one O26), and two by Listeria. The pathogen was isolated from an implicated food in 11 multistate outbreaks: 5 caused by Salmonella (alfalfa sprouts [2 outbreaks], ground turkey, shell eggs, frozen meal) and 6 caused by Shiga toxin-producing E. coli (ground beef [2 outbreaks], unpasteurized Gouda cheese, multiple unpasteurized cheeses, hazelnuts, and cookie dough).

When requested, CDC provides technical consultation and assistance to state and local public health agencies during outbreaks. CDC provides diagnostic support to confirm foodborne outbreaks. We also work to improve state and local capacity to track, investigate, diagnose, and control illnesses.

What Can Be Done

Everyone has a role in food safety. CDC has many partners, including state and local health officials, regulators, consumers, industry, clinicians, veterinarians, and educators. Together, we can:

Track, Report, and Train Others about Foodborne Disease Outbreaks

• Report suspected outbreaks to your local health department.
• Investigate outbreaks thoroughly to identify sources and improve control strategies.
• Use what is learned from outbreaks to develop new and improve existing prevention strategies.
• Develop new tools and programs, such as FoodCORE,- the Foodborne Diseases Centers for Outbreak Response Enhancement to better detect, investigate, respond to, and control multistate outbreaks.
• Keep good records of where foods and food ingredients come from.
• Train and certify managers in food safety in all restaurants.

Know the risks

• Refrain from preparing food for others if you have diarrhea or vomiting.
• Prepare food carefully for children, pregnant women, those in poor health, and older adults.
• Avoid raw (unpasteurized) milk or other dairy products made with raw milk. (Raw milk cheese that has been aged for 60 days is considered safe.)

Everyone can

• Report suspected illness from food to your local health department to help officials identify outbreaks.
• Visit FoodSafety.gov for the latest information on preventing foodborne illness.
  • Clean. Wash hands, cutting boards, utensils, and countertops.
  • Separate. Keep raw meat, poultry, and seafood separate from ready-to-eat foods.
  • Cook. Use a food thermometer to ensure that cooked foods reach a safe internal temperature:  145°F for whole meats (allowing the meat to rest for 3 minutes before carving or consuming), 160°F for ground meats, and 165°F for poultry.
  • Chill. Keep your refrigerator below 40°F and refrigerate food that will spoil.

More Information

• CDC Vital Signs for Food Safety: Making Food Safer to Eat
• CDC and Food Safety
• Foodborne Disease Outbreak Surveillance
• National Outbreak Reporting System
• Norovirus
• Foodborne Disease Burden
• Multistate Foodborne Outbreaks
• Handwashing: Clean Hands Save Lives
• Put Your Hands Together [PODCAST - 3:48 minutes]