Scientists have shared details of how they are going about updating foodborne infection figures that will be published by the World Health Organization (WHO) in 2025.
As part of the process to update estimates on the burden of foodborne diseases published in 2015, WHO is conducting a global source attribution study. Presenters in a recent webinar gave an overview of source attributions methods, the one being used for the next edition of the WHO estimates, and how the study is currently being conducted. The U.S. Food and Drug Administration is participating.
“Why do we want to do this? A risk-based approach to food safety is about allocating what are often very limited resources to the biggest problems and those that we can do the most about. Attribution informs those decisions at the large scale and also for targeted risk management decisions and this kind of work can be used to evaluate whether or not the interventions that we do undertake are effective,” said Michael Batz, senior policy advisor in the human foods program, at the U.S. Food and Drug Administration (FDA).
“We worry about foodborne diseases that are caused by a bunch of different pathogens but we don’t generally regulate pathogens. We have to target specific food products and we have to determine where in the farm to fork spectrum that we are going to intervene. Sometimes we have to determine whether the issue is in our domestic food supply or is it imported?”
Source attribution methods include retrospective analysis of surveillance data, epidemiological studies of sporadic disease, microbial subtype modeling, predictive microbiology (risk assessment), intervention studies, and structured expert judgement.
Batz said there are different methods because the kinds of decisions they are trying to inform are different and the complicated chain of how pathogens make their way to individuals.
“Some of these methods are going to be better suited for understanding major transmission pathways and others are going to be useful to attributing to specific food exposures. The reliability and availability of data is often the biggest driver as well as the computing resources and analytical expertise. There is a lot of focus on sporadic disease studies and microbial sub typing methods which are incredibly powerful but often not feasible given the data and resource requirements.”
Selected approach
Sara Monteiro Pires, chair of the source attribution task force of WHO’s Foodborne Disease Burden Epidemiology Reference Group (FERG), explained why such work was important.
“A hazard is often caused by consumption of contaminated foods but it can also be caused by other routes of transmission such as environmental contamination, direct contact with live animals or person to person transmission. If we want to define priorities for our food safety strategies we need to understand what’s the relative importance of each of these transmission routes, as well as specific foods, for any given infection?,” said Pires, who is also a senior researcher at the Technical University of Denmark.
“Source attribution is an essential step in the efforts to estimate the global burden of foodborne diseases. Structured expert elicitation provides a transparent way of obtaining source attribution and it makes it possible for us to have estimates for the proportion of specific diseases as well as transmission pathways at the global level.”
There are two steps of source attribution. The first is to understand the proportion of the burden caused by food in general as opposed to other sources. Then comes estimating what is the relative contribution of specific foods.
Pires said for global source attribution, expert elicitation is the most useful method. It has the advantage of being able to cover all regions and hazards and was also the method applied for the first FERG estimates in 2015. In the current work, more than 800 experts applied and 263 were recruited.
FERG has seven task forces: enteric disease, parasitic disease, chemicals and toxins, source attribution, computational, impact measurement, and country support.
WHO launched a call for data on foodborne outbreaks in 2023. Analysis of submitted information is ongoing but has highlighted substantial data gaps in terms of representativeness of regions and countries.
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