CDC report highlights Norovirus, Salmonella and restaurants as key

The Centers for Disease Control and Prevention’s (CDC) annual Foodborne Disease Outbreak Report, published in September 2019, has provided data on the 841 foodborne disease outbreaks that occurred throughout the US in 2017, resulting in 14,481 illnesses, 827 hospitalisations, 20 deaths, and 14 food recalls. The statistics provided some eye-opening information, particularly with regards to Salmonella, the Norovirus, and restaurants.

Although Listeria was a key focus of the US Food and Drug Administration (FDA) “swabathons” in 2017, and there was a major E. coli leafy greens outbreak, the two most frequently reported confirmed causes of outbreaks and associated illnesses that year were actually Norovirus and Salmonella.

Norovirus was the cause of:

• 140 outbreaks, 35 percent of confirmed single-pathogen outbreaks
• 4,092 illnesses, 46 percent of confirmed single-pathogen illnesses
• 40 hospitalisations, six percent of confirmed single-pathogen, outbreak-related hospitalisations
• Four deaths, 20 percent of outbreak-related deaths.

Salmonella was the cause of:

• 113 outbreaks, 29 percent of confirmed single-pathogen outbreaks
• 3,007 illnesses, 34 percent of confirmed single-pathogen illnesses
• 472 hospitalisations, 66 percent of confirmed single-pathogen, outbreak-related hospitalisations
• Eight deaths, 40 percent of outbreak-related deaths.

Additionally, Salmonella was responsible for 63 percent of all multistate outbreaks (20 of the 32 multistate outbreaks). The food source of these was confirmed in 12 outbreaks, suspected in six, and not identified in two. Salmonella was also the most cited of confirmed pathogen-food pairs responsible for the most illnesses, hospitalisations, and deaths. These included:

• Illnesses from Salmonella in turkey (580), fruits (421), chicken (299)
• Hospitalisations from Salmonella in fruits (124), kratom powder (54), vegetable row crops (35)
• Deaths from Salmonella in fruits (two).

Although E. coli (STEC) and Listeria were not listed as top causes in 2017, they were the second and third leading causes of multistate outbreaks, with E. coli implicated in six and Listeria in five. Moreover, they led to deaths, with Listeria causing three outbreak-related fatalities and E. coli, one. Additionally, E. coli caused 513 illnesses and 111 hospitalisations.

Related to specific foods, the single food categories associated with the most outbreaks were Mollusks, such as oysters (41 outbreaks), fish (37), chicken (23), and beef (19).

Outbreak environments

In addition to summarising the pathogens and foods associated with outbreaks, the report assessed outbreak settings. It discovered that restaurants were linked to outbreaks more often than any other place where food was prepared. This is not a new statistic, nor does it seem that there has been much change in the intervening years, as a high percentage of foodborne illness is still caused by mishandling in food service facilities and homes.

Of the 761 outbreaks and 12,502 illnesses in 2017 with a reported single location where food was prepared, 489 outbreaks (64 percent) and 5,533 associated illnesses (44 percent) were attributed to foods prepared in a restaurant. Most (366) occurred at establishments with sit-down dining.

While the report provides significant data for assessing and prioritising food risk, CDC cautions that the findings do have limitations. Firstly, only a small proportion of foodborne illnesses are identified as being associated with outbreaks, thus these may or may not reflect the statistics of sporadic (non-outbreak) foodborne illness or outbreaks that are not identified, investigated, or reported.

Secondly, many outbreaks had an unknown etiology and/or food. Thirdly, because agencies can submit, change, or delete reports in CDC’s outbreak surveillance system at any time, this analysis might differ from other reports. And lastly, agents not currently known to cause illness are sometimes reported as a confirmed or suspected etiology.

CDC’s Foodborne Disease Outbreak Report summarises data from the Foodborne Disease Outbreak Surveillance System, as submitted by state, local, and territorial public health agencies to the National Outbreak Reporting System (NORS), a platform for reporting enteric (gut) disease outbreaks due to food, water, animals and their environments, and from person-to-person transmission. The full 15-page report is available online.