US CDC Foodborne Disease Outbreak Information 2009-2015
On July 27, 2018, the US Centers for Disease Control and Prevention (CDC) published a summary of its foodborne disease surveillance data relating to the period 2009 to 2015.
The CDC defines a foodborne disease outbreak as, “the occurrence of two or more cases of similar illness resulting from ingestion of a common food”.1 During this period there were 5,760 reported outbreaks of foodborne disease, resulting in 100,939 illnesses, 5,699 hospitalizations, and 145 deaths. In this article, we look at the data to see what it can tell us about foodborne diseases in the United States.
The CDC began collating information on foodborne outbreaks in the early 1960s, initially through a standardized form submitted voluntarily by state, local and territorial health authorities. Since 2009, the CDC’s Foodborne Disease Outbreak Surveillance System (FDOSS), part of the National Outbreak Reporting System (NORS), has collected data via a web-based platform.
Norovirus was found to be the most serious cause with 38% of outbreaks and 41% of the illnesses. Salmonella came second with 30% of outbreaks and 35% of illnesses. When looking at the data for hospitalizations and deaths, 82% of cases could be contributed to Listeria monocytogenes, Salmonella and Shiga Toxin producing Escherichia coli (STEC). The full impact of these diseases can sometimes be hidden as, while Listeria monocytogenes only accounted for about 1% of the outbreaks, it also accounted for 51.7% of deaths – 75 of a total of 145 deaths recorded during the period 2009-2015.
Other causes of outbreaks included:
- Campylobacter - 5%
- Clostridium perfringens - 4%
- Scrombroid toxins such as histamine - 3%
- Ciguatoxin - 3%
- Staphylococcus aureus - 1%
- Vibrio parahaemolyticus - 1%
The US CDC has traced these outbreaks to many sources such as mycotoxins, puffer fish tetrodotoxin, paralytic shellfish poisoning, pesticides, amnesic shellfish poison and various parasites such as cryptosporidium, trichinella, cyclospora and giardia. While none are very significant in the percentage of outbreaks and illnesses, mycotoxins resolved in 3% of the deaths, the same as are attributed to Clostridium perfringens.
The report details 2,442 (42%) outbreaks where investigators identified food as a cause, of which 1,281 cases implicated a single food. The top three foods associated with outbreaks were fish (17%), dairy (11%) and chicken (10%). Top three foods associated with illness were chicken (12%), pork (10%) and seeded vegetables (10%). The link between outbreak and illness becomes clearer when you look at the pairings of pathogen to foodstuff – fish with scrombroid toxins and ciguatoxins, dairy with Campylobacter, and Salmonella with chicken.
Salmonella has been identified as a serious source of outbreak and illness partly because it can be found on a wide variety of foodstuffs – for example, eggs, seeded vegetables, chicken and pork. Salmonella combined with these four foodstuffs have been identified as the top four reasons for hospitalization due to foodborne illness. Salmonella and STEC were the two most common causes of large outbreaks.
Listeria monocytogenes, the cause of 75 deaths, has been linked to the consumption of fruit, dairy and vegetable crops. In 2011, 28 states were affected by Listeria monocytogenes attributed to cantaloupes, resulting in 33 deaths, and in 2014 another 12 states were affected by infections attributed to caramel apples.
Several novel food outbreaks are also reported, including the raw wheat flour outbreak of 2015, which contained STEC serogroups O26 and O121. Other outbreaks from novel sources included chia seed powder (Salmonella serotypes Gaminara) and moringa leaf powder (Salmonella serotype Virchow). These outbreaks show that Salmonella and STEC can survive extensive processing and the period these products are in a dried state.
Unfortunately, in 58% of the outbreaks and 49% of the illnesses there is no food reported. This creates of void of information and therefore hinders those involved in providing resolutions to potential problems that are not being detected.
This pathogen is the leading cause of outbreaks and foodborne illnesses. Most cases are caused by infected workers in restaurants or other food service settings contaminating ready-to-eat foods during preparation. Specific foods implicated in norovirus outbreaks and illnesses include raw leafy vegetables, fruit and mollusks.
The location of the outbreak has a severe affect upon the statistics. Due to the definition of foodborne disease used by the CDC, outbreaks and illnesses are unlikely to be reported if they take place in a domestic setting. In the majority of cases, unless a person seeks medical attention, it will simply be dealt with by the family. This will be the case with many norovirus outbreaks. Even so, the house is still reported as the location for 12% of outbreaks and 10% of the illnesses.
Commercial enterprises are, however, still the dominant location identified in the report. Restaurants are reported in 61% of outbreaks and 43% of illnesses – the majority being sit-down restaurants. In addition, catering or banquet facilities account for 14% of outbreaks and 24% of illnesses. If combined in institutional locations such as schools, offices, prisons camp or day care locations have more illnesses (13%) than homes, but fewer outbreaks (4%). The location of an outbreak cause was not known 13% of the time and this was attributed to 13% of the overall illnesses.
Problems in the Data
The CDC acknowledges limitations in its report. For example, in a third of outbreaks the food and/or cause of the outbreak remains unknown. While reporting has steadily increased from 2009 to 2015, some States – because of financial conditions or regulatory department organizational structures – are better staffed with personnel, or have the latest technology such as whole genes sequencing, which enable quicker investigations which in turn help them to identify the source and cause of the outbreak data. The CDC also acknowledges that because the majority of foodborne illness occur outside of a recognized outbreak, its data showing approximately 15,000 illnesses per year and 800 yearly outbreaks, may be very far from accurate. Instead, it estimates that true number may be approximately 9.4 million illnesses each year.
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