Foodborne Infections in 2023: No Progress Toward U.S. Goals — or Just Better Tests?

Reducing foodborne and enteric disease is a public health priority. Healthy People 2030 set reduction goals for Campylobacter, Listeria, Salmonella and Shiga toxin–producing E. coli (STEC), measured against average yearly incidence in 2016–2018. CDC's Foodborne Diseases Active Surveillance Network (FoodNet) tracks progress by monitoring infections from eight pathogens commonly spread through food. These are its preliminary 2023 results.

The network

FoodNet does active, population-based surveillance for laboratory-diagnosed Campylobacter, Cyclospora, Listeria, Salmonella, Shigella, STEC, Vibrio and Yersinia infections, and for hemolytic uremic syndrome (HUS) in children — a possible complication of STEC — at 10 U.S. sites. It is a collaboration of CDC, 10 state health departments, the U.S. Department of Agriculture's Food Safety and Inspection Service and the Food and Drug Administration.

In 2023, for the first time since 2004, it expanded to cover all of Colorado. It now represents 16% of the U.S. population (53.6 million people), against 15% (51.0 million) for the historic area. The expansion added representation of Hispanic (8% more), American Indian or Alaska Native (8%), Native Hawaiian or Pacific Islander (6%) and rural (10%) residents — groups the historic area had underrepresented or held too few of to study.

2023 at a glance

In the historic area FoodNet counted 29,607 infections, 7,234 hospitalizations and 177 deaths (in the expanded area, 31,492, 7,588 and 184). 15% were linked to international travel. Campylobacteriosis was most common, then salmonellosis and STEC infection.

Compared with 2016–2018, domestically acquired infections:

Crude incidence in the historic area; "up" means a substantial increase by the report's Bayesian model.

Listeria is rare but serious: 97.5% of its patients were hospitalized, and 22.5% of domestic cases died.

The testing shift

More and more infections are diagnosed by culture-independent diagnostic tests (CIDTs) rather than by growing the germ.

• In 2023, 78% of bacterial infections were diagnosed by CIDTs, 46% by CIDT alone.
• Reflex cultures — attempts to grow the germ after a positive CIDT — fell from 71% of CIDT diagnoses in 2016–2018 to 68%, most for Yersinia, Vibrio and STEC.
• For every illness except listeriosis, fewer reflex cultures succeeded than in earlier years.

Without an isolate, a germ cannot be speciated, serotyped or serogrouped, so the share of infections traced to a specific species, serotype or serogroup was lower than in any previous year, and infections left untyped rose substantially.

• Salmonella: of 8,454 infections, 83% gave an isolate and 89% of those were fully serotyped. Enteritidis and Newport, the most common serotypes, were stable; Typhimurium, Javiana and I 4,[5],12:i:- fell substantially.
• STEC: of 3,351 infections, only 57% gave an isolate, and 87% of those were fully serogrouped. O157 fell; non-O157 was stable.

Children with HUS

In 2022, the latest year available, FoodNet found 61 cases of post-diarrheal HUS in people under 18, 39 of them under 5. Incidence — 0.6 per 100,000 under 18 and 1.4 under 5 — was stable against 2016–2018.

What it means

The lack of progress may reflect testing, not more disease. CIDTs speed diagnosis and treatment and find infections that would once have gone undetected — their spread has been linked to marked rises in reported incidence. But their use varies over time, by lab and by pathogen, which clouds the trends, and some have high false-positive rates for certain germs, such as Vibrio.

Fewer isolates also mean less material for subtyping, whole genome sequencing and antimicrobial resistance testing. That could weaken outbreak detection and source tracing, spotting of emerging drug resistance, and tracking of specific strains. Raising successful reflex culture rates is a public health priority that needs effort and resources at federal, state and local levels. Continued surveillance is needed to follow the effect of changing tests, and targeted prevention is needed to cut disease.

Limits

• Only people who seek care and are tested are counted.
• The underlying reason for a hospitalization or death may be unknown, and deaths more than a week after specimen collection or discharge may be missed.
• People with unknown travel status are counted as domestic, which may overstate domestic cases.

Sources

Based on Shah HJ, Jervis RH, Wymore K, et al., "Reported Incidence of Infections Caused by Pathogens Transmitted Commonly Through Food: Impact of Increased Use of Culture-Independent Diagnostic Tests — Foodborne Diseases Active Surveillance Network, 1996–2023," MMWR Morbidity and Mortality Weekly Report, volume 73, Centers for Disease Control and Prevention; a work of the United States government in the public domain.