Examining vulnerability to foodborne illness: A comprehensive review of “clinically vulnerable groups"

A total of 660 definitions relating to ‘clinically vulnerable groups’ and ‘at-risk populations’ were obtained and reviewed. These definitions came from 20 of the 36 national and global food safety organisations that were identified by the research team. Examples of how clinically vulnerable groups were defined in some of the reviewed resources included:

“Children under 5-years-old, pregnant women, the elderly, and people with weakened immune systems (like people with cancer or other diseases) have a higher risk of getting a bad Salmonella infection and can die if their symptoms are severe.” (U.S. Food and Drug Administration, 2024).

“Listeriosis is rare but for pregnant women, the elderly and people with weak immune systems the illness can be serious and fatal Listeria may cause pregnant women to miscarry or the baby can be born prematurely or stillborn.” (Food Standards Australia New Zealand, 2024). 

“Young children, people aged 65 or over, and those whose immune systems are not working properly have a greater risk of becoming severely ill with food poisoning caused by salmonella.” (Food Standards Agency, 2023).

“Raw milk remains an inherently risky product that poses particular dangers to specific groups of people – namely children, pregnant women, older people or those who are unwell or have chronic illness.” (Safefood, 2023).

“Older adults, infants, and persons with weakened immune systems are more likely to develop a severe illness.” (U.S. Department of Agriculture Food Safety and Inspection Service, 2024).

A third of the definitions came from the US (n=217 definitions) (Table 20), these included definitions from organisations including the Centers for Disease Control and Prevention (CDC), U.S. Food and Drug Administration (FDA), Food Safety and Inspection Service (FSIS), Center for Food Safety and Applied Nutrition (CFSAN), the Partnership for Food Safety Education (PFSE) and the U.S. Department of Agriculture (USDA).

As also indicated in Table 20, the two organisations that most frequently referred to clinically vulnerable groups in their resources were Health Canada and the Food Safety Authority of Ireland (FSAI). As part of the review, 98 definitions were obtained from the UK, of these, 35 came from Food Standards Scotland (FSS), others came from the Advisory Committee on the Microbiological Safety of Food (ACMSF) (n=31), the Food Standards Agency (FSA) (n=24), UK Health Security Agency (UKHSA) (n=5) and the Department for Environment, Food and Rural Affairs (DEFRA) (n=3).

As indicated in Figure 2, 14% of the reviewed documents that defined clinically vulnerable groups did not have a publication or update date available. Of the remainder, 42% were published or updated in the previous 5 years, 291 of the definitions were in resources that were published up to 24 years ahead of the review.

The most common types of resources that definitions were obtained from included consumer advice (32%), general information pages (29%) and reports (such as risk assessment) (27%). Other resources included guidance for industry, healthcare, or educational institutions (Table 21).

Of the 660 definitions relating to clinically vulnerable groups and at-risk populations that were reviewed, the pathogen most frequently referred to was L. monocytogenes, with 293 of the definitions (44%) specifically referring to the pathogen. As indicated in Table 22, 140 definitions (21%) referred to Salmonella, fewer referred to E. coli (n=90/14%), Campylobacter (n=60/9%) and norovirus (n=56/8%). One hundred and forty-nine of the resources that defined clinically vulnerable groups did so in relation to generic foodborne illnesses or referred to “food poisoning”.

Among the groups defined as being clinically vulnerable, one or more of the groups collectively described as the YOPI fraction (young (0-5 years), older (65+ years), pregnant, and immunocompromised) (Denayer et al., 2017; Gray et al., 2024) were included in 100% of the definitions.

As illustrated in Table 23, older adults were most frequently referred to, which were included in 96% of the definitions. Nearly three-quarters (72%) of the definitions referred to people with weakened immune systems, 64% referred to pregnant individuals and/or their unborn children, 52% referred to children and 35% referred to neonates or newborns. Indeed, these groups do include persons that are often highly susceptible to infection and generally suffer much more serious illness than other members of the community.

Further breakdown of the data as indicated in Table 24 and in Appendix 6 indicates that 40% of the definitions specifically referred to the risk of listeriosis among pregnant individuals (40%), older adults (37%) and those with weakened immune systems (34%).

Older adults

Older adults were the group most frequently referred to in relation to clinically vulnerable groups at risk of foodborne illness (96% of all definitions), furthermore, as indicated in Table 24, in relation to each of the five pathogens of interest, older adults were most frequently referred to in relation to Campylobacter (70%), Salmonella (86%) and non-specific foodborne pathogens (81%). Although 90% of sources referring to listeriosis referred to pregnant individuals and their unborn babies, 83% of definitions for clinically vulnerable groups relating to listeriosis referred to older adults. 
Various terms were used to refer to older adults including seniors, elderly, and ageing populations. Of the 559 definitions that referred to older adults, 25% referred to a specific age, as indicated in Figure 3, the most common age banding given for older adults was ≥65 years (70%), 18% referred to ≥60 years.

Children

Children were more commonly referred to in relation to E. coli (90%), Salmonella (75%), and non-specific foodborne illness (80%). Children were only referred to in 8% of definitions relating to L. monocytogenes and 27% of definitions regarding norovirus. A total of 339 definitions referred to children, 32% of these specified an age. As indicated in Figure 4, the ages given varied, however the majority (80%) referred to children under the age of five years old.

Most definitions were generic and referred to multiple groups. Six percent of definitions (n=41) were specifically targeting a defined clinically vulnerable group and 8% of definitions (n=51) gave specific advice for different clinically vulnerable groups, such as specific food products that pregnant individuals should avoid.
Of the 660 definitions reviewed, it was determined that 42% did not provide context as to why individuals are vulnerable or at increased risk of foodborne illness, 49% simply stated that it was ‘because of a weakened immune system’. Sixty-two definitions (9%) provided context, the majority of these referred to children, pregnant individuals, and people receiving chemotherapy treatment, for example:

“Food poisoning can be especially severe for infants because their digestive and immune systems are immature.” (NSW Food Authority, No date).

“Young children make less stomach acid that kills harmful bacteria, making it easier for them to get sick.” (U.S. Food and Drug Administration, 2022).

“Your baby or toddler is at increased risk for foodborne illness. Young children do not have fully developed immune systems. They may be more likely to become ill, have serious complications and have a harder time getting well.” (Partnership for Food Safety Education, no date).

“When you’re pregnant, hormonal changes in your body lower your immune system which can make it harder to fight off illness and infection.” (New South Wales Food Authority, No date).

“You and your growing fetus are at high risk from some foodborne illnesses because during pregnancy your immune system is weakened, which makes it harder for your body to fight off harmful foodborne microorganisms Your unborn baby’s immune system is not developed enough to fight off harmful foodborne microorganisms. For both mother and baby, foodborne illness can cause serious health problems — or even death.” (Center for Food Safety and Applied Nutrition, no date).

"If you are a cancer patient, your healthcare provider may have recommended that you receive chemotherapy, radiation, or other treatments to help fight your disease. A weakened immune system can be a side effect of these types of therapies. A properly functioning immune system works to clear infection and other foreign agents from the body. However, cancer and its treatments can weaken your immune system, making you more susceptible to many types of infections." (U.S. Department of Agriculture Food Safety and Inspection Service, 2020).

Very few described why older adults are at an increased risk of foodborne illness, for example:

“Among the elderly, the risk increases as individuals age, i.e., as compared to healthy individuals 40 to 59 years of age, Canadian data show that persons aged 65 to 69 years of age have a 4-times increased risk, while those aged 75 to 79 years of age have nearly a 9-times increased risk (PHAC, 2009b).” 

Although these rare examples do provide some context, it is unclear to what extent consumers understand the details, and therefore, we believe this merits further exploration.

Most definitions (64%) did not provide references or sources of information, 19% referred to previous research with references, the remainder referred to other information sources such as organisation landing pages.