Foodborne Illnesses Hit 24,000 Americans in 2016

Bridget M. Kuehn

April 20, 2017

In 2016, 24,029 people reported foodborne illnesses, according to the Centers for Disease Control and Prevention's (CDC's) Foodborne Surveillance Network (FoodNet). Campylobacter and Salmonella were the most common cause of infection. However, increasing use of rapid tests to diagnose foodborne infections may be obscuring some patterns of disease, CDC experts cautioned.

In addition to the overall case number, the report, published in the April 21 issue of the Morbidity and Mortality Weekly Report, notes there were 5512 hospitalizations and 98 deaths attributed to foodborne pathogens.

Foodborne infections remain a major cause of illness in the United States, but these illnesses often go unreported. To track such infections and identify potential sources of infection, the CDC's FoodNet program collects data from sites in 10 states that test samples for foodborne pathogens. Together, FoodNet sites cover approximately 15% of the US population.

The latest FoodNet report shows that Campylobacter (8547) and Salmonella (8172) were the leading cause of such infections in 2016, followed by Shigella (2913), Shiga toxin-producing Escherichia coli (1845), and Cryptosporidium (1816). Yersinia, Vibrio, Listeria, and Cyclospora were also reported, but with about 300 or fewer cases each.

"This report provides important information about which foodborne germs are making people sick in the United States," said Robert Tauxe, MD, MPH, director of the CDC's Division of Foodborne, Waterborne, and Environmental Diseases, in a news release. "It also points out changes in the ways clinicians are testing for foodborne illness and gaps in information as a result."

Increasing use of rapid diagnostic tests, called culture-independent diagnostic tests (CIDTs), for detecting foodborne illnesses led the CDC for the first time to report how many infections were diagnosed only by CIDTs. The tests may improve treatment by allowing faster diagnosis, according to the CDC. However, these tests do not provide enough information to identify antibiotic-resistant strains or to track whether a single strain is linked to a larger outbreak. Follow-up tests in which the bacteria are cultured are needed to provide this valuable information, but only 60% of the CIDT results were accompanied by a follow-up test, according Ellyn P. Marder, MPH, from the CDC's Division of Foodborne, Waterborne, and Environmental Diseases, and colleagues note in the report.

"It's important that laboratories continue to do follow-up cultures on CIDT-positive patients so public health officials can get the information needed to protect people from foodborne illness," Dr Tauxe said.

In addition, the new tests may be leading to diagnoses in cases that would previously not have been tested, so the testing change may skew the results. Thus, it is difficult to accurately compare the 2016 results to those from years in which CIDTs were not used as frequently.

Despite acknowledging these limitations, Marder and colleagues did identify a few trends in the data. For example, Salmonella typhimurium infections declined 18% in 2016 compared with the average for 2013 to 2015. This decline may have been driven by new pathogen-reduction requirements for raw poultry products implemented by US Food Safety and Inspection Service in early 2016, according to the report.

In addition, cases of Yersinia, Cryptosporidium, and Shiga toxin-producing E coli infections increased, but the authors suggest these increases were likely a result of increased use of the rapid tests.

The report emphasized the need for continuing prevention efforts.

"Most foodborne infections can be prevented, and substantial progress has been made in the past in decreasing contamination of some foods and reducing illness caused by some pathogens," write Marder and colleagues. "More prevention measures are needed."

The authors have disclosed no relevant financial relationships.

Morb Mortal Weekly Rep. 2017;66:397-403. Full text

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