New global foodborne diarrheal disease burden estimates for 2021, which will serve as inputs for the World Health Organization’s (WHO’s) forthcoming updated, broader estimates of the global burden of foodborne diseases, have been published.

WHO’s Foodborne Disease Burden Epidemiology Reference Group (FERG) published its previous foodborne disease burden estimates in 2015. FERG reconvened in 2021–2025 to update these estimates, which are set to be published in 2026. The newly released research on the foodborne diarrheal disease burden supports FERG’s work.

Estimates Based on the Largest Database to Date

The current report on diarrheal disease burden includes three new pathogens—rotavirus, Cyclospora cayetanensis, and Enteroaggregative Escherichia coli (EAEC)—in addition to the nine pathogens included in previous reports: thermophilic Campylobacter, Cryptosporidium, Entamoeba histolytica, enteropathogenic (EPEC), enterotoxigenic E. coli (ETEC), Shiga toxin-producing Escherichia coli (STEC), Giardia, norovirus, nontyphoidal Salmonella, Shigella, and Vibrio cholerae.

According to the researchers, the latest estimates are based on the largest database of pathogen detection rates compiled to date.

The estimates are based on a literature review and meta-analysis of publications that reported the prevalence of cases of diagnosed illness, including stool samples from asymptomatic subjects, community-detected and outpatient diarrhea cases, and inpatient cases.

Foodborne Pathogens Caused 2.2 Billion Diarrheal Diseases and 880,000 Deaths 

The researchers estimated that, globally, the 14 pathogens were responsible for 2.2 billion diarrheal disease cases and 880,000 deaths in 2021. The largest number of cases occurred in Southeast Asia and the largest number of deaths occurred in Sub-Saharan Africa, while Europe experienced the lowest number of illnesses and fatalities.

Shigella Emerges as New Top Cause of Disease

The leading causes of diarrheal morbidity were bacterial infections in 2021, with the exception of the protozoan Giardia, which caused 321.2 million cases. Specifically, Shigella caused 426.4 million cases, Campylobacter caused 21.4 million, and ETEC caused 259.7 million. This is a departure from previous estimates, which ranked rotavirus and norovirus highest. Notably, the 2021 estimates support a much higher morbidity burden for Shigella than previous reports (which estimated an incidence rate of 5,400 per 100,000), due to the high population attributable fractions (PAFs) in outpatients aged five years or older.

Rotavirus Named Most Deadly

Rotavirus was the leading cause of diarrhea mortality in 2021, causing 214,700 deaths, followed by Shigella (152,500) and V. cholerae (94,100). The ranking of V. cholerae was mainly due to its large PAF in inpatients aged five years or older and high case fatality rate.

Regional Trends: Significant Norovirus Morbidity in High-Income Countries

At the national level, Campylobacter incidence was highest in India and Pakistan, as well as in numerous countries in Africa, besides Kenya, which was an outlier of low Campylobacter incidence.

Diarrhea attributable to ETEC, Giardia, and Shigella is endemic at high levels of incidence across Sub-Saharan Africa, India, and Pakistan.

Norovirus is the only pathogen with a morbidity burden in all higher-income countries (HICs) that is comparable to that in Sub-Saharan Africa, and greater than that found in South American, North African, and Middle Eastern low- and middle-income countries (LMICs).

Salmonella has the highest incidence in the U.S., Canada, Sub-Saharan Africa, India, Thailand, and Papua New Guinea, and the lowest incidence in Russia, China, Mongolia, Central Asia, and some countries in Eastern and Southeastern Europe.

STEC incidence is lowest in HICs outside of the Americas, and highest in Sub-Saharan Africa, India, and Pakistan.

V. cholerae is endemic only in Sub-Saharan Africa, South Asia, some Middle Eastern LMICs, and the Philippines.

Limitations

The researchers urge caution when interpreting PAFs for pathogens that elicit prolonged residual shedding following resolution of symptoms (e.g., norovirus, Campylobacter, Giardia).