Estimating Foodborne Disease Burden for Public Health Policy Prioritization

How do governments obtain data that supports policy generation for public food safety? Thomas et al. (2015) present details from a study estimating the burden generated by foodborne disease (FBD) in Canada that indicates areas of concern and action¹.

In order to maintain public confidence and uphold food safety, policy makers and food industry producers need to understand what risks they face from FBD. For this reason, analyzing health records for FBD incidence and sequelae, including hospitalization and death, is valuable. Data obtained from this source indicates prevalence and pathogens implicated in addition to an estimate of the total burden imposed. From these, policy makers and other experts can direct strategy more effectively towards areas requiring the most attention. Furthermore, combined with pathogen knowledge and food product science, industry members can direct prevention efforts with greater focus.

Thomas et al. use health data collected from the Canadian Hospital Morbidity Database (CHMD) covering the years between 2000 and 2010. The team focused on estimating the burden of FBD acquired domestically, using statistics collected previously to generate data². Taking the population of Canada in 2006 (32,500,000) as the reference midpoint in the study, they combined CHMD records with pathogen-specific epidemiological knowledge to generate hospitalization and mortality figures for 30 FBD pathogens. In addition, the team also considered data showing FBD due to unspecified agents and generated estimates of burden in this category.

The Public Health Agency of Canada reports approximately 4 million cases of FBD per year. Looking at the billing and diagnostic codes in records within the CHMD, Thomas et al. aggregated cases involving domestically-acquired FBD. They based inclusion according to two approaches.

Approach 1: The researchers used diagnostic codes from the International Classification of Diseases (ICD) registries, 9^th and 10^th revisions, to search for hospitalization and death due to FBD pathogens (n=20 leading to hospitalization; n=19 leading to death).

Approach 2: Where the team identified gaps in the data that involved pathogens not identified in the CHMD, they used surveillance data and literature reports for information (n=5 pathogens leading to hopsitalization; n=10 pathogens leading to death). Thomas et al. looked at cases admitted with acute gastroenteritis that had a diagnostic suspicion of FBD.

The team used the first 16 billing codes within the CHMD for each case to enable inclusion, to define outcome and direct calculation of burden estimates. For a FBD like norovirus or rotavirus, the researchers used reports of gastrointestinal illness for case numbers and then followed up with literature reviews.

For all pathogens and cases of FBD, the research team assumed a level of under-reporting for true incidence since FBD is frequently mild and mostly self-limiting, in addition to presenting problems with absolute diagnosis. Using the estimates determined in Thomas et al. 2013, they generated factors to deal with under ascertainment, making calculations individually for each pathogen. They used these factors to scale up the case numbers determined from the laboratory-confirmed and hospital database records, noting that for certain diseases with established reporting and surveillance programs, less correction was needed.

The final numbers obtained from the database searches and application of correction factors showed that per year, FBD results in more than 11,600 hospitalizations and is responsible for 238 deaths overall. Separating results according to etiology showed that 30 identified FBD pathogens caused 4,000 hospitalizations (range = 3,200-4,800) and 105 deaths (75-139), whereas unspecified agents resulted in 7,600 hospitalizations (5,900-9,650) and 133 deaths (77-192).

FBD pathogens norovirus, non-typhoidal Salmonella species, Camplylobacter, VTEC O157, and Listeria monocytogenes accounted for 74% of hospitalizations where an agent was isolated. When an infectious agent was known, the research team calculated that bacteria caused 66% of hospitalizations and 76% of deaths, with viruses responsible for 31% and 19%, and parasites 3% and 5% respectively.

FBD pathogens causing the greatest number of deaths included L. monocytogens (n=35), norovirus (21), non-typhoidal Salmonella species (17) and VTEC O157 (8), which cumulatively covered 77% of all deaths reported.

Thomas et al. note that the method used to obtain statistics from the CHMD might also pull cases where FBD is not the primary reason for hospitalization. Overall, although determining food as the primary source for infection is problematic, the researchers are confident that the individual correction factors calculated for each FBD pathogen give results comparable to those obtained in other countries of similar development level. They suggest that more work is required to develop DALY (disability adjusted life years) indicators for sequelae to foodborne illness in Canada as a stronger indicator for priority in food safety policy development.

Learn more about foodborne pathogen testing in our food and beverage section

Reference

1. Thomas, M.K. et al. (2015) “Estimates of Foodborne Illness–Related Hospitalizations and Deaths in Canada for 30 Specified Pathogens and Unspecified Agents“, Foodborne Pathogens and Disease 12 (pp.820-7) DOI: 10.1089/fpd.2015.1966

2. Thomas, M.K. et al. (2013) “Estimates of the Burden of Foodborne Illness in Canada for 30 Specified Pathogens and Unspecified Agents, Circa 2006“, Foodborne Pathogens and Disease 10 (pp.639–48)