Burden of Foodborne Illness in the United States: Methods and Data Sources

Methods

Estimating U.S. foodborne illnesses by major pathogens

In general, for each pathogen, we gathered data from surveillance systems and corrected for underreporting and under-diagnosis.

We then multiplied the adjusted number by the proportion of illnesses that was acquired in the United States (that is, not during international travel) and the proportion transmitted by food to yield an estimated number of illnesses that are domestically acquired and foodborne.

Then, we added the estimates for each of the pathogens to arrive at a total, and we used an uncertainty model to generate a point estimate and 90% credible interval (upper and lower limits).

Estimating hospitalizations and deaths from U.S. foodborne illnesses by major pathogens

In general, for each pathogen, we multiplied the estimated number of reported illnesses (after correcting for underreporting) by the pathogen-specific hospitalization and death rate from surveillance data, surveys, or outbreak data.

Because some people with illnesses that were not laboratory-confirmed would also have been hospitalized and died, we doubled the estimates to correct for under-diagnosis.

We multiplied the adjusted hospitalization and death estimates by the proportion of illnesses that were acquired within the United States (vs. international travel-related) and the proportion transmitted by food.

Finally, we used an uncertainty model to generate a point estimate and 90% credible intervals for both hospitalizations and deaths.

Data sources

We used data from a variety of sources and studies.

Surveillance systems

• Foodborne Disease Outbreak Surveillance System (FDOSS)
• Foodborne Diseases Active Surveillance Network (FoodNet)
• Listeria Initiative

Surveys

• FoodNet Population Survey
• FoodNet Laboratory Survey
• National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP)

Vital (government) statistics

• National Center for Health Statistics multiple-cause-of-mortality data
• U.S. Census

Scientific publications

• Structured Expert Judgement for attribution of illness transmitted by food (Beshearse et al. Emerg Infect Dis. 2021 Jan;27(1):182-195)
• Active surveillance from Kaiser Permanente Northwest (Burke et al. Clin Infect Dis. 2021 Aug 16;73(4):e913-e20).
• Administrative data from MarketScan® Commercial and Medicare Supplemental Databases (Burke et al. Clin Infect Dis. 2021 Jul 1;73(1):e1-e8.)

Improvements

Improvements compared with previous studies

CDC's earlier estimates used the best data sources and methods at the time. New surveillance data, methods, and other factors have contributed to more accurate estimates for 2019.

• New data and methods have become available.
• New regulations and other interventions to prevent foodborne illness have been implemented.
• Culture-independent diagnostic tests (CIDT) have been more widely adopted, increasing the likelihood of identifying pathogens.

Additionally, the current methods use better data sources and improved methods for adjusting for under-diagnosis.

Need for improvements and innovations remains

Future investments and innovations in surveillance and data analysis could help increase the accuracy of estimates.

Future efforts can also be directed toward quantifying the illnesses caused by long-term effects of foodborne infections and to estimate the economic costs associated with foodborne illness.

Dive deeper

• Read the publication: Foodborne illness acquired in the United States—Major pathogens, 2019
• Get answers to commonly asked questions