Foodborne Infections in FoodNet's 10 U.S. Sites, 2018: Most on the Rise

Foodborne disease is a major health problem in the United States. CDC's Foodborne Diseases Active Surveillance Network (FoodNet), part of its Emerging Infections Program, tracks laboratory-diagnosed infections with eight pathogens commonly spread through food, in 10 sites covering 15% of the U.S. population — approximately 49 million people in 2017. The sites are Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado and New York. FoodNet is a partnership of CDC, 10 state health departments, the USDA's Food Safety and Inspection Service (FSIS) and the Food and Drug Administration (FDA).

This preliminary 2018 report found 25,606 infections, 5,893 hospitalizations and 120 deaths, with most infections becoming more common.

The 2018 numbers

Campylobacter and Salmonella had the highest incidence. The rises for Cyclospora, Vibrio, Yersinia, STEC, Campylobacter and Salmonella were statistically significant.

• Salmonella: of 7,013 isolates serotyped (87%), the most common were Enteritidis (2.6 per 100,000), Newport (1.6) and Typhimurium (1.5), much as in 2015–2017.
• STEC: 440 of 1,570 isolates tested (28%) were O157. Among 662 non-O157 isolates serogrouped, O103 (31%), O26 (28%) and O111 (24%) led. Neither O157 nor non-O157 incidence changed.
• Hemolytic uremic syndrome — a complication of STEC marked by renal failure, thrombocytopenia and microangiopathic anemia — was found in 54 children in 2017 (0.49 per 100,000), 36 of them (67%) under 5 (1.22 per 100,000), no different from 2014–2016.

The testing shift

Clinical labs increasingly use culture-independent diagnostic tests (CIDTs), which find pathogens that older methods missed but make trends harder to read. In 2018 the number of bacterial infections diagnosed by CIDT rose 65% over the 2015–2017 annual average, from 29% for STEC to 311% for Vibrio.

DNA-based syndrome panels diagnosed 68% of Yersinia and 67% of Cyclospora infections, falling to 2% for Listeria. A follow-up "reflex" culture was attempted on 75% of CIDT-positive specimens, from 64% for Campylobacter to 100% for Listeria, and when tried it grew the pathogen from 100% of Listeria and 86% of Salmonella specimens down to 37% for Vibrio.

Infections diagnosed by culture or by CIDT, by pathogen, year and culture status, 2015–2018. CDC.

Where the infections come from

• Campylobacter, FoodNet's most common infection since 2013, causes diarrhea, sometimes bloody, and rarely Guillain-Barré syndrome, an autoimmune paralysis. Poultry is a major source: under a new FSIS test method introduced in August 2018, it was isolated from 18% of chicken carcasses and 16% of chicken parts sampled. FSIS plans updated contamination standards.
• Salmonella Enteritidis has not declined in over 10 years. It is adapted to poultry, and eggs are an important source. FDA's Egg Safety Rule, in place by 2012, requires preventive measures and refrigeration on farms with 3,000 or more hens; a 2018 multistate outbreak came from a farm that had grown past that size without adopting them. Chicken meat matters too: in December 2018 FSIS reported that 22% of establishments producing chicken parts failed the Salmonella standard. Typhimurium, by contrast, fell in poultry and in people, possibly because of changes in poultry production, including vaccination against it; in the United Kingdom, vaccinating chickens against Enteritidis, with better hygiene, was followed by a marked fall in human cases.
• Produce: romaine lettuce was linked to two multistate STEC O157 outbreaks in 2018, and produce outbreaks plus wider use of syndrome panels likely explain the Cyclospora jump. FDA is helping industry task forces on romaine safety, labeling and traceability, expanded sampling of imported and domestic produce in 2018, and is implementing the Produce Safety Rule, with inspections of large farms.

Limits and next steps

• Changing tests make trends harder to read: rises may come partly or wholly from what clinicians order and from panels that catch what culture missed.
• Some CIDT results may be false positives.
• Big outbreaks cause year-to-year swings that may not last.

Getting and subtyping isolates is a growing burden on state health departments, but it is essential for spotting outbreaks and judging prevention. Suggested measures include tackling Campylobacter on chicken, stronger egg-production safeguards (especially in small flocks), vaccinating poultry against Enteritidis, reducing Salmonella on produce, poultry and meat, and continuing to implement the Food Safety Modernization Act's Produce Safety Rule.

Sources

Based on Tack DM, Marder EP, 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, 2015–2018," MMWR Vol. 68, No. 16, CDC; a work of the United States government in the public domain. CDC later published an erratum for this report. The report gives Campylobacter's 2018 incidence as 19.5 per 100,000 in its text and 19.6 in its table; neither is given here.