It is not possible to accurately compare foodborne disease rates between countries, according to the Food Standards Agency (FSA).

The agency, which covers England, Wales and Northern Ireland, said this is because of different methodologies and recording systems. The FSA estimates there are about 2.4 million cases of foodborne illness every year in the United Kingdom.

Researchers compared how different countries estimate how many people suffer food poisoning each year to try and determine whether these rates can be reliably compared. The study, funded by the FSA and done by Public Health England, found three approaches.

Countries calculate foodborne disease estimates because of under-reporting, as not everyone who gets ill will seek medical help and those who do will not always get a confirmed diagnosis. Data can be used to inform a country’s policy and prioritize resources.

A different study, published this year, estimated there are 180 deaths per year in the UK caused by foodborne diseases from 11 pathogens. The U.S. Centers for Disease Control and Prevention (CDC) projected in 2011 there were 2,612 deaths for 31 pathogens commonly transmitted by food.

“An almost impossible task”
Rick Mumford, FSA head of science, evidence and research, said attempting to accurately compare different countries’ foodborne disease rates was an “almost impossible task.”

“The only way you could attempt this would be for different countries to have the same type of study with the exact same study specifications, over the same time period. Even then, differences in underlying surveillance data available in each country could cause issues, particularly in terms of determining what proportion of infectious intestinal disease cases are due to food,” he said.

Studies used to estimate Infectious Intestinal Disease (IID) and foodborne disease fall within three categories: retrospective cross-sectional, prospective cohort, and surveillance pyramid studies. However, methodologies vary among and within countries. The FSA uses the prospective cohort approach.

The first and second of these approaches estimate IID from all sources including food and non-food, so another step of mathematical models is added to estimate the proportion of illness due to foodborne disease.

Detail on the approaches
Cross-sectional retrospective studies are the most common. These are wher a representative sample of the population are contacted and asked about symptoms in the recent past. However, differences in study design such as case definitions, recall periods and representativeness of population samples can affect incidence rates.

Prospective cohort studies involve recruiting a sample population in advance. Participants are required to report on a weekly basis if they had symptoms of diarrhea and vomiting. For most such studies, those reporting symptoms submit stool samples for microbiological examination so the case of illness can be determined. Few of these studies have been done because they can be expensive, participations rates can be low and people lost to follow-up. However, they are the most accurate way of estimating IID rates of the three methods because samples from symptomatic patients are obtained to confirm any hypothesis.

Surveillance pyramid studies predict the number of cases, hospitalizations and deaths due to foodborne pathogens. It involves estimating the number of infections missed through under diagnosis and underreporting. However, the models are country specific so cannot reliably be used for other nations.

More research planned
In total, 33 studies were included in the review between January and July 2019; 19 were retrospective, cross-sectional surveys, six cohort studies, five surveillance pyramid studies and three could not be grouped into these categories. All selected articles were published between 1994 and 2017. Researchers focused on eight pathogens known to cause the greatest burden in the UK.

These retrospective, cross-sectional population level based surveys were conducted in the UK, Germany, Poland, Denmark, Italy, Sweden, Ireland, Australia, Norway, Canada, France, New Zealand, United States and the Netherlands.

The six studies that used a prospective cohort design were in the UK, Sweden and Netherlands. The five efforts using surveillance data and population surveys were in the U.S., Canada, Australia, New Zealand, and UK.

The FSA is planning to start a third IID study in 2021. In the coming months, the agency will publish two more projects. One to analyze foodborne disease rates in the UK, US, Australia and Canada in more detail and the other looking at food production methods worldwide, to help inform understanding of different systems.