Brian Morgan – The reasons why food poisoning is frequently linked to eating chicken – Sep 2025
There are two main types of bacteria, campylobacter and salmonella, that are linked to food poisoning. They both live normally in the gut of chickens without harming the birds, but they will cause illness, normally gastroenteritis, if they get into the gut of humans. The severity of the illness varies enormously between people, but can be very troublesome, particularly for children under 2 years and old people and those whose health is compromised in some way.
Transmission from chickens is usually due to poor hygiene when handling and preparing raw chicken meat for eating or from insufficient cooking, but infection can also arise from pets that are carrying the bacteria, and from contaminated water. When travelling abroad, stomach upsets are often due to these bacteria.
Campylobacter is around eight times more common in poultry gut than is salmonella, and it is thought to affect well over half a million people in the UK per year. The infection can last up to a fortnight, but little treatment is available, so many people do not report it.
About 300,000 infections are reported by those who become infected, and about 30,000 cases a year are treated at a cost to the health services of an estimated £55 million annually. The total cost to society is estimated at about £700 million annually, and about 20 people die each year from campylobacter infection as the main cause.
Campylobacter, alongside norovirus, is the most prolific foodborne disease in the UK, thus suggesting that proper procedures to protect us from infection by campylobacter are not being diligently followed.
Medical research In the modern era has identified a large number of antibiotics, but most of them have been used to excess and the development of antimicrobial resistance now makes most of them ineffective. As a result, most infections are no longer treated by the same antibiotics that were used before. When a campylobacter infection requires treatment there are two groups of antibiotics , azithromycin (e.g. ciprofloxacin) and the fluoroquinolones, that are usually used but resistance to fluoroquinolones is now common.
It is probably not surprising that antibiotic resistance is now occurring in the fluoroquinolones. This is because they have been widely used in intensive poultry farms around the world, including the UK, and it has been found that antibiotic resistance has developed to them in those intensive poultry farms. As a result, the resistance that has developed due to over-use in intensive poultry farms is likely to have been passed on, via poultry meat, into the wider world.
There are two species of campylobacter to be found in poultry, both with a fairly similar level of pathogenicity and ability to cause the same type of illnesses. They are Campylobacter jejuni and Campylobacter coli. C. jejuni is approximately ten times more common than C. coli in poultry. In the case of C. jejuni, the bacteria produce a toxin in the human gut whose activity is similar to that of the cholera toxin.
Salmonella has a number of different strains, including those related to typhoid diseases. All can be prevented by vaccination should you think you are likely to be exposed to them. Fortunately, the salmonella strain in poultry that affects humans the most is non-typhoidal salmonella.
In recent years there has been a huge increase in intensive poultry farming, especially broilers (chickens bred and reared for their meat). Currently about one billion broiler and egg-laying birds are raised every year by the UK’s intensive poultry farms. This escalation has happened over the last twenty years, and has been in close parallel with the increase in cases of campylobacter .
In particular, there has been a growth in the establishment of very large poultry farms, known as mega-farms. The definition of such a farm, based on the United States definition, is farms with 125,000 or more broiler chickens or 82,000 egg-laying chickens. The way these mega-farms are run greatly affects the degree of transmission of diseases, particularly of campylobacter and salmonella.
The number of campylobacter cases, and of salmonella too, have been rising recently and there is a strong possibility that this is linked to the large rise in poultry consumption in the UK. Chicken is now the most commonly eaten meat, and accounts for over 40% of meat consumption.
I believe the reason for the recent substantial increases in foodborne illnesses, and particularly of campylobacter, must be connected to the parallel rise in intensive broiler poultry rearing, and especially the practice of in bulk high-speed slaughter at abbatoirs where the bacteria in the gut is transferred onto the outer reaches of the carcass. The carcass is steam washed, but in the UK that wash is not chlorinated, and around two out of every three carcasses sold at retail have campylobacter bacteria present, and in around one in five affected carcasses it is at a high level.
The stock in intensive broiler poultry units is generally replaced ten times per year, and on each occasion the removal and safe disposal of bedding and faeces demands full sterilisation of the unit, see here. Nevertheless, questions continue to be asked about the efficiency of this cleansing.
The fact remains that many birds leaving broiler intensive farms are infected with campylocater, and standards will inevitably vary, both at the farms and at the slaughter houses. For example, at the slaughter house the practice of holding carcasses vertically encourages leakage from the gut, which ought really to be bound at the throat after slaughter. The leakage spills onto the skin of the carcass, and is also scattered further during the de-feathering process.
Like most bacteria, campylobacter also forms biofilms. Biofilms are communities of particular bacteria which develop a strong outer shield (film) that enables the bacteria to live for a long time in the environment and, in the case of campylobacter, especially on the surfaces of food processing plants and in the food chain. Their outer coat (film) also protects them against outside stresses as they move from place to place, and protects them against external changes in temperature and moisture and, also, antimicrobial resistance is able to develop further inside biofilms.
Completely erasing foodborne illness will never be possible. However, we can minimise our exposure to them by high standards of hygiene when preparing food, and by asking government and food producers to observe the highest standards in the methods and procedures affecting food production.
If we do not, the incidence of foodborne illnesses will continue to rise, as they are doing at present.
References:
1. Proceedings of the Royal Society, 2022. A Restatement of the natural science evidence base regarding the source, spread and control of campylobacter species causing human disease.
https://ora.ox.ac.uk/objects/uuid:5ba28269-1f73-4188-a9bb-d5f8fdeae461
2. The prevalence of Campylobacter spp. in broiler flocks and on broiler carcases, and the risks associated with highly contaminated carcases
3. Poultry Science, 2025: Research Note: Gut instincts: Salmonella contamination based on monitoring systems in the broiler sector.
https://www.sciencedirect.com/science/article/pii/S003257915000859#
