VOL: 97, ISSUE: 22, PAGE NO: 54
Paul Sudworth, FIBMS, DMLM, is chief biomedical scientist, Microbiology Department, Scarborough and Northeast Yorkshire Healthcare NHS Trust
Campylobacter are microscopic bacteria 0.3-0.6mm in diameter and 2-3mm in length. The name Campylobacter is derived from the Greek campylos, meaning ‘curved’, and baktron, meaning ‘rod’. When stained with Gram’s stain they appear as a spiral Gram-negative bacillus.
Campylobacter was first isolated from aborted sheep foetuses in 1909 and given its current name in 1963. These organisms cause two major groups of disease: foetal infections in cattle and sheep and acute enterocolitis in humans. It was only in the 1970s that the role of Campylobacter as an enteropathogen came to light and laboratories routinely began to isolate them. The genus Campylobacter consists of 14 species, of which two, C. jejuni (enteric disease) and C. fetus (extraintestinal disease), are most commonly encountered in human disease. C. fetus is mainly seen as a cause of abortion in sheep and sporadic abortion in cattle. Human infections with C. fetus are limited to systemic infections in patients with underlying immunodeficiency or serious disease. Rarely are they seen in cases of human abortion.
In the laboratory, faecal samples are routinely investigated for many bacterial pathogens, such as salmonella, shigella, Campylobacter, Escherichia coli 0157, several viruses and a range of parasites. Campylobacter are grown on a selective culture medium containing antibiotics to inhibit growth of normal faecal flora and incubated at 42oC for 48 hours in a micro-aerophilic atmosphere in a sealed jar. Any suspicious growth is stained by the Gram’s method and the identity confirmed with a few simple tests.
Sources of Campylobacter
Campylobacter is a worldwide zoonosis (animal diseases that can be transmitted to man) and is commonly found in the gastrointestinal tract of a wide range of animals, including cattle, sheep, domestic pets, rodents and all varieties of fowl. Campylobacter is particularly associated with birds and this is the largest reservoir, domestic poultry being especially prone to colonisation. This is a major source of human infection.
Why do we become infected with Campylobacter?
The important factors to consider when investigating the cause of gastrointestinal infections are the origin of the organism and the means of transmission.
In developed countries the cause of disease is usually direct ingestion of contaminated food, while in developing countries contaminated water is often a source.
Meat from infected animals frequently becomes contaminated with faecal material during the slaughtering process. Commercially raised poultry are often colonised with C. jejuni. Slaughterhouse procedures can spread contamination and so chicken and turkey in supermarkets may be frequently contaminated. Infected animal excreta may also contaminate soil or water. C. jejuni survives in milk, other foods and water at 4oC for several weeks. Pasteurisation effectively destroys the organism, as does chlorine at concentrations used for water disinfection. Cases of Campylobacter infection have been seen in milk delivered to the door where birds have pecked the foil seals and consequently contaminated the milk.
Raw and undercooked meat (especially poultry) is the main source of infection in the home. Simple precautions practised in the kitchen can avoid contracting Campylobacter from raw meat. Rules for general hygiene in the kitchen apply for all food poisoning organisms (Box 1).
Increases in Campylobacter infections are seen through the summer months and to some extent may reflect the use of barbecues, when outer surfaces of the meat can easily become burnt and give the false impression of adequate cooking.
If you become infected with Campylobacter the incubation period is usually two to five days but can be from one to 11 days. The common clinical features are abdominal pain, profuse diarrhoea and malaise; vomiting is uncommon. The disease is usually self-limiting, with symptoms lasting from one day to one week or longer, and the organism is excreted in the faeces for an average of two to three weeks.
Diarrhoea may range in severity from loose stools to massive watery or grossly bloodstained stools. Many patients experience 10 or more bowel movements on the worst days of symptoms. The predominant manifestation of the illness is abdominal pain. As young adults are commonly affected, the characteristics of clinical symptoms may be confused with ulcerative colitis or Crohn’s disease. In common with some other organisms causing gastro-enteritis, Campylobacter may cause pseudoappendicitis; in most cases the correct diagnosis is made during the postoperative period when diarrhoea continues.
Bacteraemia is seen in fewer than 1% of patients with C. jejuni infection and is more common in patients at the extremes of age. One interesting uncommon consequence of C. jejuni infection (one case per 2,000 infections) is the Guillain-Barre syndrome (GBS), a severe neurological disease. Between 20-50% of GBS cases follow C. jejuni infections (Blaser, 2000).
There were 55,000 Campylobacter infections reported to the Public Health Laboratory Service (PHLS) in the UK in 1999. These are the proven cases of Campylobacter isolated from stools of patients and where environmental health has been notified. It is thought that the actual number of people infected could be 10 times higher due to some people not visiting their doctor and underreporting through environmental health and the PHLS.
Campylobacter infections causing gastroenteritis in uncomplicated cases are usually self-limiting; they resolve without treatment, as is the case with other organisms, such as salmonella. The most appropriate treatment is fluid and electrolyte replacement. In serious cases intravenous solutions of fluid and electrolytes may be required. With less serious volume depletion oral rehydration using glucose and electrolyte solutions may be indicated.
Antibiotic treatment has its place with certain groups of patients - those presenting with high fever, bloody diarrhoea and more than eight stools a day, patients whose symptoms have not lessened or are worsening, or those who have had symptoms persisting for more than a week. The antibiotic of choice in these cases is erythromycin, with ciprofloxacin a useful alternative.
Using erythromycin in cases of Campylobacter infection has been shown to eliminate carriage within 72 hours in most patients, unlike infections with salmonella, where use of antibiotics in uncomplicated cases may prolong the period of carriage.
Patients with immunodeficiency are particularly at risk from severe complications of Campylobacter infections. Fatal cases of C. jejuni septicaemia in patients with AIDS have been reported, where a clinical picture of fulminant septic shock despite therapy has been seen (Manfredi et al, 1999). Campylobacter are important opportunist pathogens in HIV disease, causing septicaemic illness.
Antibiotics in the food industry
One practice in the food industry which is causing concern is the feeding of antibiotics to animals to reduce infection rates in flocks and so allow more rapid weight gain. In the USA the Food and Drug Administration (FDA) is considering banning the use of the antibiotic enrofloxacin in poultry. The reason for this is the increasing number of Campylobacter carried by chickens becoming resistant to this antibiotic. Bacteria resistant to enrofloxacin are also resistant to ciprofloxacin, one of the antibiotics favoured for treatment of Campylobacter infection in humans. The FDA is concerned that antibiotic-resistant Campylobacter from chickens might cause antibiotic-resistant infections in humans. In England and Wales around 15% of human Campylobacter infections are resistant to ciprofloxacin(Public Health Laboratory Service, 2000).
The important message here is that enrofloxacin and all other antibiotics used in veterinary and human medicine must be used very carefully if we are to limit the development of resistant bacteria which is increasingly becoming a serious problem hindering the treatment of human infection. The British Veterinary Association and drug companies have now released guidelines on the careful use of antibiotics in veterinary medicine.
Campylobacter remains a significant cause of bacterial gastroenteritis and without vigilance in our food industry and the safe preparation of food in the home this is unlikely to change.