What is Campylobacter?
Campylobacter is a genus of Gram-negative, spiral-shaped bacteria containing at least 16 different species, some of which, especially C. jejuni, but also C. coli, C. lari, C. hyointestinalis and C. upsaliensis, may cause gastroenteritis in humans. Campylobacter is now the leading cause of bacterial gastroenteritis in many developed countries.
Campylobacter is unique amongst food poisoning bacteria in that it is not normally able to grow and multiply in foods. This is mainly because it has specific atmospheric requirements (reduced levels of oxygen) for growth and can only multiply at relatively high temperatures.
What foods can be contaminated?
Campylobacter is most often associated with fresh poultry meat. A UK Food Standards Agency study in 2007/2008 found that the level of poultry carcass contamination in the UK was 65.2%, and studies elsewhere have also found contamination rates of at least 60 %, with up to 10 million Campylobacter cells per carcass being recorded. Fresh poultry is more frequently and more heavily contaminated than frozen.
Campylobacter species have also been isolated from other fresh meats such as beef, lamb, pork and offal – though at lower frequencies than in poultry – and occasionally in raw milk, shellfish, mushrooms and salads.
How does it affect health?
Campylobacter species can cause gastrointestinal infections. The infective dose is small, possibly less than 500 cells, and symptoms appear between 1 to 11 days (typically 2 – 5 days) after infection. The symptoms can vary widely and usually start with muscle pain, headache and fever. Diarrhoea is very common, and both blood and mucus may be present in stools. Nausea also occurs, but vomiting is rare. Some people experience severe abdominal pain, which can be confused with appendicitis. Symptoms can last from 1 to 7 days (typically 5 days), but the infection is usually self-limiting and death is rare, particularly in otherwise healthy individuals. Children under five and young adults are most frequently affected.
Occasionally, campylobacteriosis can lead to complications, such as types of arthritis (e.g. Reiter’s syndrome). Reactive arthritis occurs in 1 % of cases and 0.1 % can suffer Guillain-Barré syndrome; a severe neurological disorder, which can lead to paralysis.
How common is illness?
Campylobacter is now recognized as the main cause of bacterial gastroenteritis in Europe, with nearly 200,000 cases being reported in the EU in 2008. The majority of these are thought to be foodborne. In the USA, the organism is estimated to be responsible for 2.4 million cases of illness and 124 deaths each year. Other developed countries report a similar picture. In 2008, New Zealand was reported to have the highest incidence of Campylobacter infection in the developed world.
Most cases of Campylobacter enteritis are sporadic, or part of small family-related outbreaks, so that sources of infection are difficult to identify. However, most cases are thought to be associated with undercooked, or recontaminated, poultry meat. Large outbreaks are quite rare, but have been linked to raw milk, poultry liver pâté, salads, raw clams, garlic butter, fruits and contaminated water. In one incident in 2005, at least 80 people working at offices in Copenhagen were made ill by contaminated chicken salad in canteen meals.
Where does it come from?
Campylobacter species are found in the intestinal tract of many warm-blooded animals, including cattle, sheep, pigs, goats, dogs and cats, but are especially common in birds. Wild birds are thought to be a reservoir for domestic and food animals.
Infected humans can transfer Campylobacter to food via the faecal/oral route when personal hygiene is poor. Excreta from infected animals can contaminate water and mud, and Campylobacter can survive for some time in these environments, particularly when temperatures are low.
How is it affected by environmental factors?
Campylobacter is unable to grow and multiply at the temperatures normally used to store food. The temperature range for growth is 30 – 45°C, with an optimum of 42°C. Survival at room temperature is poor, but Campylobacter can survive for a short time at refrigeration temperatures – up to 15 times longer at 2°C than at 20°C. The bacteria die out slowly at freezing temperatures.
Campylobacter is heat sensitive and the cells are destroyed at temperatures above 48°C. They do not therefore survive the normal pasteurization processes applied to milk. Moderate cooking processes targeted at other food poisoning bacteria (e.g. Salmonella) will easily inactivate Campylobacter.
The optimum pH for growth is 6.5 – 7.5, and Campylobacter does not grow in culture below pH 4.9. The cells die out rapidly at pH values less than 4.0, especially above refrigeration temperatures.
The minimum water activity for growth is around 0.987 (equivalent to 2% sodium chloride). The cells are sensitive to salt and, depending on temperature, levels of 1% or more can be bactericidal (less effect at lower temperatures). Although Campylobacter is sensitive to dry conditions, it may survive for some time on wooden cutting boards.
Campylobacter is microaerophilic, requiring reduced levels of oxygen (5 – 6 %) to grow. The cells usually die out quickly in air, but survive well in some modified atmosphere or vacuum packaging.
How can it be controlled?
For food processors
Poultry and poultry products are considered to be the main source of Campylobacter food poisoning and controls focus on minimizing the level of contamination during the production and processing of poultry meat.
In many European countries measures are in place to encourage effective biosecurity and hygiene strategies to prevent poultry flocks becoming infected. For example, in Denmark, ‘Campylobacter-free’ chicken meat can be marketed, providing that it comes from flocks meeting required standards.
Much attention has also been given to measures designed to reduce high rates of cross contamination during the processing of poultry, particularly chicken, by improving the hygienic design and operation of equipment such as de-feathering machines and immersion chiller tanks.
For retailers and consumers
Although Campylobacter is unable to grow in foods stored at normal temperatures, the low infective dose means that undercooking of raw foods and/or cross contamination from raw to ready-to eat foods is a major risk factor for human infection.
Clear and effective instructions can help to ensure that the pathogen is destroyed during the cooking stage. Undercooking and/or cross contamination at barbeques are thought to be at least partly responsible for an increase in reported Campylobacter infections during the summer months.
Consumer education and domestic hygiene training can help prevent the transfer of Campylobacter from raw to ready-to-eat foods. Consumers should be advised not to wash meat and poultry carcasses prior to cooking to prevent water droplets from contaminating kitchen surfaces. Any potentially contaminated surfaces, such as chopping boards, should be thoroughly disinfected after use.
Are there rules and regulations?
No specific requirement is made under EU legislation with regard to levels of Campylobacter species in food. Requirements for their control are covered under EU general food safety requirements.
The UK Health Protection Agency (HPA) has published guidelines on acceptable levels of microorganisms in various ready-to eat foods. These state that ready-to-eat foods on the market should be free from thermotolerant Campylobacter spp. and that their presence in ready to eat foods is ‘unsatisfactory: potentially injurious to health’ and/or the product is unfit for human consumption.
Where can I learn more?
Risk assessment of Campylobacter spp. in broiler chickens. World Health Organization. (2009).
Risk Profile: Campylobacter jejuni/coli in poultry (whole and pieces). Institute of Environmental Science and Research Limited. (March 2007).
Advisory Committee on the Microbiological Safety of Food. Second Report on Campylobacter. (2005).