Foodborne Infections in 2019: Progress Has Stalled

CDC's Foodborne Diseases Active Surveillance Network (FoodNet), part of its Emerging Infections Program, tracks laboratory-diagnosed infections from eight germs commonly spread by food, at 10 U.S. sites covering about 15% of the population — an estimated 49 million people in 2018. It is a partnership of CDC, 10 state health departments, the USDA's Food Safety and Inspection Service and the FDA. A team led by Danielle M. Tack reported the preliminary 2019 data, compared with 2016–2018.

The headline: none of the eight got better. Five rose and three were unchanged, meaning progress against major foodborne pathogens has stalled and the Healthy People 2020 targets would not be met.

2019 by the numbers

25,866 infections, 6,164 hospitalizations and 122 deaths.

Source: CDC, MMWR.

Campylobacter and Salmonella caused the most illness. Listeria is rare, but nearly everyone infected was hospitalized and 16% died.

Newer tests change the picture

Many labs now use culture-independent diagnostic tests (CIDTs), which detect a germ's genetic material or antigens without growing it. Bacterial infections diagnosed by CIDT rose 32%. The share diagnosed only that way ranged from 57% for Yersinia to 1% for Listeria. Some of the rise in infections likely reflects these tests catching cases that used to go undiagnosed — but that cannot explain the overall lack of progress.

The catch is that CIDTs don't produce a bacterial isolate, and isolates are needed for whole genome sequencing (WGS). In 2019, public health labs completed the switch from pulsed-field gel electrophoresis to WGS for subtyping bacteria, which better detects outbreaks, resistance and emerging strains. Labs attempted culture on 75% of positive CIDT results. Getting full value from WGS requires culturing CIDT-positive samples.

Salmonella: a tale of serotypes

Among fully typed Salmonella isolates, the most common serotypes were Enteritidis (2.6 per 100,000), Newport, Typhimurium, Javiana, I 4,[5],12:i:- and Infantis.

• Enteritidis has been the leading serotype since 2007 and isn't declining. Eggs were its main source in the 1980s, and chicken was recognized as another in the late 1990s.
• Typhimurium fell 13% and has dropped from the most common serotype in 1996–1998 to third. Heidelberg, once third, is no longer in the top 20. Vaccinating chickens against Typhimurium — which shares antigens with Heidelberg — may be part of the reason.
• Infantis rose 69%, from ninth most common in 1996–1998 to sixth, much of it a new, highly drug-resistant strain found in chicken.

After the United Kingdom vaccinated chickens widely and improved farm hygiene, its Enteritidis infections dropped sharply — suggesting poultry vaccination against other serotypes could cut U.S. illness too.

E. coli, produce and Cyclospora

STEC O157 infections fell 20%, but non-O157 STEC rose 35%, and outbreaks linked to leafy greens continue. Produce is also an important source of Cyclospora, Listeria and Salmonella. Wider use of multi-pathogen test panels may partly explain the huge jump in Cyclospora, but more exposure can't be ruled out. Continued enforcement of FDA's Produce Safety Rule, including more inspections of domestic and imported produce, and new prevention approaches are needed.

In 2018, FoodNet recorded 62 cases of post-diarrheal hemolytic uremic syndrome (HUS) — a kidney-failing complication of STEC — in children, half of them under 5; rates were unchanged from 2015–2017.

Limitations

Part of the increase is likely due to CIDTs finding previously missed infections, and to changes in testing practices and test accuracy; changes in health care use or the population may also play a role; and one year's change may not signal a lasting trend.

Sources

Based on Tack DM, Ray L, Griffin PM, et al., "Preliminary Incidence and Trends of Infections with Pathogens Transmitted Commonly Through Food — Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2016–2019," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain.