Highlights from the 2017 Surveillance Report

When two or more people become ill from eating the same contaminated food or drink, the event is called a foodborne disease outbreak.

Outbreaks are caused by pathogens, which include germs (bacteria, viruses, and parasites), chemicals, and toxins. Although most foodborne illnesses are not part of a recognized outbreak, outbreaks provide important insights into how pathogens are spread, which food and pathogen combinations make people sick, and how to prevent foodborne illnesses.

Each year, CDC summarizes foodborne disease outbreak data in an annual surveillance report and makes the data available to the public through the NORS Dashboard.

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Main Findings

In 2017, 841 foodborne disease outbreaks were reported by 50 states, Washington, D.C., and Puerto Rico, resulting in 14,481 illnesses, 827 hospitalizations, 20 deaths, and 14 food recalls.

Single food categories associated with the most outbreak-related illnesses:
- Turkey (609 illnesses)
- Fruits (521 illnesses)
- Chicken (487 illnesses)
- Pork (376 illnesses)
Single food categories associated with the most outbreaks:
- Mollusks, such as oysters (41 outbreaks)
- Fish (37 outbreaks)
- Chicken (23 outbreaks)
- Beef (19 outbreaks)
Restaurants were linked to outbreaks more often than any other place where food was prepared, as in previous reports. Restaurants were associated with 489 outbreaks, accounting for 64% of outbreaks that had a single location where food was prepared. Most of these restaurant outbreaks (366, 48% of outbreaks) occurred at establishments with sit-down dining.
Thirty-two multistate outbreaks were reported. Of the 25 multistate outbreaks linked to a single category of food, 17 involved categories implicated in more than one outbreak:
- Fruits (10 outbreaks)
- Vegetable row crops, such as leafy greens (5 outbreaks)
- Dairy (2 outbreaks)

Main Findings

In 2017, 841 foodborne disease outbreaks were reported by 50 states, Washington, D.C., and Puerto Rico, resulting in 14,481 illnesses, 827 hospitalizations, 20 deaths, and 14 food recalls.

Single food categories associated with the most outbreak-related illnesses:
- Turkey (609 illnesses)
- Fruits (521 illnesses)
- Chicken (487 illnesses)
- Pork (376 illnesses)
Single food categories associated with the most outbreaks:
- Mollusks, such as oysters (41 outbreaks)
- Fish (37 outbreaks)
- Chicken (23 outbreaks)
- Beef (19 outbreaks)

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Restaurants were linked to outbreaks more often than any other place where food was prepared, as in previous reports. Restaurants were associated with 489 outbreaks, accounting for 64% of outbreaks that had a single location where food was prepared. Most of these restaurant outbreaks (366, 48% of outbreaks) occurred at establishments with sit-down dining.
Thirty-two multistate outbreaks were reported. Of the 25 multistate outbreaks linked to a single category of food, 17 involved categories implicated in more than one outbreak:
- Fruits (10 outbreaks)
- Vegetable row crops, such as leafy greens (5 outbreaks)
- Dairy (2 outbreaks)

Other Highlights

A single pathogen was confirmed as the cause in 395 outbreaks. The most commonly reported pathogens were:

Norovirus (140 outbreaks, 35% of confirmed single-pathogen outbreaks)
Salmonella (113 outbreaks, 29% of confirmed single-pathogen outbreaks)

A single pathogen was confirmed as the cause in 8,954 outbreak-related illnesses, 719 hospitalizations, and 20 deaths. The most common causes of outbreak-related illnesses were:

Norovirus (4,092 illnesses, 46% of confirmed single-pathogen illnesses)
Salmonella (3,007 illnesses, 34% of confirmed single-pathogen illnesses)
Shiga toxin-producing Escherichia coli (STEC) (513 illnesses, 6% of confirmed single-pathogen illnesses)

Of the 719 outbreak-related hospitalizations attributed to a single confirmed pathogen, the pathogens that caused the most hospitalizations were:

Salmonella (472 hospitalizations, 66% of confirmed single-pathogen, outbreak-related hospitalizations)
STEC (111 hospitalizations, 15% of confirmed single-pathogen, outbreak-related hospitalizations)
Norovirus (40 hospitalizations, 6% of confirmed single-pathogen, outbreak-related hospitalizations)

The pathogens that caused outbreak-related deaths were:

In addition, one death occurred in an outbreak caused by Salmonella, Clostridium perfringens, Bacillus cereus, and Staphylococcus aureus. The pathogen or pathogens that caused the death were not reported.

Investigators were able to identify the food that made people ill in 43% of outbreaks (360 outbreaks). The food could be placed into one of 24 possible categories in more than half of those outbreaks (218 outbreaks). Of the 218 outbreaks where the food could be categorized, the most commonly implicated food categories were:

Mollusks (41 outbreaks, 19% of outbreaks that could be categorized)
Fish (37 outbreaks, 17% of outbreaks that could be categorized)
Chicken (23 outbreaks, 11% of outbreaks that could be categorized)
Beef (19 outbreaks, 9% of outbreaks that could be categorized)

Outbreaks in which the food could be categorized resulted in 3,795 illnesses. These outbreak-associated illnesses were most commonly from:

Turkey (609 illnesses, 16% of illnesses)
Fruits (521 illnesses, 14% of illnesses)
Chicken (487 illnesses, 13% of illnesses)
Pork (376 illnesses, 10% of illnesses)

Knowing which pathogen and food combinations make people sick is important for preventing outbreaks because they help identify how food gets contaminated and what actions are needed to make it safer.

The confirmed pathogen-food pairs responsible for the most outbreaks were:

Scombroid toxin (histamine poisoning) in fish (17 outbreaks)
Ciguatoxin in fish (13 outbreaks)
Salmonella in chicken (11 outbreaks)

The confirmed pathogen-food pairs responsible for the most illnesses, hospitalizations, and deaths were:

Illnesses
- Salmonella in turkey (580 illnesses)
- Salmonella in fruits (421 illnesses)
- Salmonella in chicken (299 illnesses)
Hospitalizations
- Salmonella in fruits (124 hospitalizations)
- Salmonella in “other” foods (54 hospitalizations in a single outbreak that implicated kratom powder)
- Salmonella in vegetable row crops (35 hospitalizations)
Deaths
- Salmonella in fruits (2 deaths)

Among the 761 outbreaks and 12,502 illnesses with a reported single location where food was prepared, 489 outbreaks (64%) and 5,533 associated illnesses (44%) were attributed to foods prepared in a restaurant. Among these single-location outbreaks, restaurants with sit-down dining were most commonly reported as the location where food was prepared (366 outbreaks, 48% of the outbreaks).

Product recalls occurred in 14 outbreaks:

In 2017, there were 32 multistate outbreaks (4% of all reported outbreaks). Multistate outbreaks resulted in 1,118 illnesses (8% of illnesses), 327 hospitalizations (40% of hospitalizations), and 4 deaths (20% of deaths).

Pathogens responsible for multistate outbreaks:

Salmonella (20 outbreaks)
STEC (6 outbreaks)
Listeria (5 outbreaks)
Vibrio parahaemolyticus (1 outbreak)

Foods implicated in multistate outbreaks were classified as confirmed or suspected based on the evidence available. For multistate Salmonella outbreaks, the food source was confirmed in 12, suspected in 6, and not identified in 2. Foods confirmed in multistate outbreaks of Salmonella:

Foods suspected in multistate Salmonella outbreaks:

For multistate STEC outbreaks, a food source was confirmed in 2 outbreaks, suspected in 3, and not identified in 1. Foods confirmed in multistate outbreaks of STEC:

Leafy greens (serogroup O157)
Soy butter (serogroup O157)

Foods suspected in multistate STEC outbreaks:

Leafy greens (serogroup O157)
Flour (serogroup O121)
Spinach (serogroup O157)

For multistate Listeria outbreaks, a food source was confirmed in 1 outbreak, suspected in 2, and not identified in 2. Ready-to-eat pork products were the confirmed food source in a multistate outbreak of Listeria.

Foods suspected in multistate Listeria outbreaks:

Caramel apples
Pasteurized cheese

Raw oysters were the confirmed food source in the outbreak of Vibrio parahaemolyticus.

Fourteen multistate outbreaks investigated in 2017 are not included in 2017 data because the first outbreak-associated illness occurred before 2017. Outbreaks were only included if the first illnesses occurred in 2017. Salmonella caused 10 of those outbreaks, with chicken, ground beef, and papaya confirmed as the source in 3 outbreaks. Chicken was suspected in 1 outbreak. In 6 outbreaks, no food was identified. In 8 of these Salmonella outbreaks, the first illnesses began in 2016. In 2 of the outbreaks with no food identified, illnesses began in 2015.

Listeria caused the remaining 4 outbreaks. A source was confirmed for only 1 outbreak: artisanal soft cheese (first illness in 2015). Suspected sources for the other three outbreaks were hummus (first illness in 2013), queso fresco (first illness in 2014), and smoked fish (first illness in 2014).

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More Information

Foodborne diseases due to known germs (bacteria, viruses, and parasites) are estimated to cause 9.4 million illnesses each year in the United States. Even though only a small proportion of these illnesses occur as part of a recognized outbreak, the data collected during outbreak investigations provide insights into the pathogens and foods that cause illness. Public health officials, regulatory agencies, and the food industry can use these data to help make food safer.

The data from this report come from CDC’s Foodborne Disease Outbreak Surveillance System (FDOSS). State, local, and territorial health departments report the results of foodborne disease outbreak investigations to this system, and CDC provides an annual summary of outbreak investigations.

When comparing data between years, it is important to note that changes were made to this surveillance system in 2009, and a new food categorization scheme was implemented in 2011.

The findings in this report have at least four limitations. First, only a small proportion of foodborne illnesses that occur each year are identified as being associated with outbreaks. The degree to which the foods, pathogens, and locations implicated in outbreaks represent the food sources, pathogens, and locations of sporadic (non-outbreak) foodborne illness is unknown. Similarly, not all outbreaks are identified, investigated, or reported. Second, many outbreaks had an unknown etiology (cause), an unknown food, or both, and may not be similar to those outbreaks in which an etiology or food could be identified. Third, CDC’s outbreak surveillance system is dynamic. Agencies can submit new reports and change or delete reports as information becomes available. Therefore, the results of this analysis might differ from those in other reports. Finally, agents not known to cause illness are sometimes reported as a confirmed or suspected etiology.

NORS Dashboard is CDC’s interactive online program for searching and accessing data submitted through the National Outbreak Reporting System (NORS), including data in the Foodborne Disease Outbreak Surveillance System. NORS Dashboard lets readers search foodborne disease data by year, state, food and ingredient, location where food was prepared, and pathogen. It provides information on numbers of illnesses, hospitalizations, deaths, and the confirmed or suspected cause.

For guidance on using the data and limitations to keep in mind when searching by food or ingredient, look at frequently asked questions about NORS Dashboard.

Surveillance for Foodborne Disease Outbreaks — United States, 2009–2015 describes 7 years of data about the causes of outbreaks, where they occur, and the foods responsible for the most outbreaks, illnesses, hospitalizations, and deaths.

Although foodborne disease outbreaks are a nationally notifiable condition, many factors can influence outbreak investigation and reporting, including available resources (such as time, staff, and laboratory capacity), health department priorities, and the characteristics of an outbreak (such as its size and severity).

Even the most thorough investigations can fail to identify the contaminated food under certain circumstances, such as when most of the people who became sick ate many of the same foods (making it hard to identify the one that caused them to become ill), the number of people ill is very small, or the outbreak is identified after people’s memories have faded of what they ate before getting sick. CDC encourages health departments to report all foodborne outbreak investigations. Even if the contaminated food is not determined, we can learn useful information about the causal pathogen of outbreaks, their settings, populations affected, and factors leading to food contamination that can help inform prevention efforts.

Even well-conducted investigations may not be able to identify the causal agent of an outbreak. Several factors influence whether investigators can identify it, including the timing of when a specimen is obtained.

Infections are often diagnosed using specific laboratory tests that can identify bacteria, chemical agents and toxins, parasites, and viruses. When an outbreak is not identified until after the optimal time to obtain specimens from ill people, it may not be possible to obtain specimens for laboratory analysis or the laboratory results may be inconclusive.
When timely specimens are obtained, other factors can lead to the causal agent not being detected. For example, clinical laboratories may not have the resources needed to identify some pathogens. In these outbreaks, the state public health laboratory or CDC may perform additional tests to try to identify the germ.

Even if the causal agent is not identified, CDC encourages states to report all foodborne disease outbreak investigations because much can be learned about the food sources of outbreaks, their settings, populations affected, and factors leading to food contamination. Public health officials, regulatory agencies, and the food industry can use these data to inform efforts to prevent foodborne illness.

Learn More About Foodborne Outbreaks

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