BACTERIAL GASTROENTERITIS

Definition: Gastroenteritis means inflammation of the stomach and small and large intestines. Bacterial gastroenteritis is an infection caused by a variety of bacterias and bacterial toxins that results in vomiting or diarrhea;including Staphylococcus, Salmonella, Shigella, Campylobacteri, Clostridium, Escherichia. coli, Vibrio spp., Bacillus aureus, Listeria monocytogenes etc. See Table for epidemiological datas.

Staphylococcus aureus: Food poisoning strains of this bacterium are probably the most common cause of food poisoning in the United Kingdom, but as the disease is relatively mild, and it generally clears up in less than a day, the majority of cases probably never get reported. Strains of Staphylococcus aureus associated with particular bacteriophage types can produce a toxin that is absorbed, and that acts upon the vomiting centre in the brain. Symptoms of staphylococcal food poisoning include vomiting that starts between 30 minutes and 6 hours following the consumption of the contaminated food. Because it can be found on human skin, staphylococci cause food poisoning in foods that require a lot of manipulation in their preparation, including cream cakes, trifles, and prawn cocktails.

Salmonella: The species of salmonella that commonly causes gastroenteritis is Salmonella enteritidis. This species is divided into over 2,000 serovars, depending upon their expression of somatic "O" and flagellar "H" antigens. Salmonella infections are associated with drinking unpasteurised milk, or with consumption of various foodstuffs, particularly poultry or poultry products. Pork pies are another potential source of salmonella infection. Salmonella typhi is a bacterium that causes an invasive, systemic infection, that may be life-threatening known as enteric fever. This is an exclusively human pathogen. This contrasts with Salmonella enteritidis, a bacterium that has a very wide distribution, and that can be isolated from reptiles as well as mammals. Salmonella typhi infections are spread by the faecal-oral route, and water that is contaminated with human faeces is the most common source.

Shigella: Bacilliary dysentery is caused by bacteria of the genus Shigella. An infectious dose of about 100 bacteria is typical of bacteria of this genus. Bacilliary dysentery is characterised by the presence of blood, pus and mucus in stools, accompanied by abdominal pain and cramps.In the developed world, Shigella sonnei is the commonest bacterium of the genus associated with dysentery. In the Third World, Shigella dysenteriae is the commonest isolate, and the cause of the most severe form of the disease. Because of the highly infectious nature of these bacteria, and due to the personal habits of small children, in the United Kingdom incidents of dysentery caused by Shigella sonnei often occur in preschool playgroups or in primary schools.

Campylobacter: Campylobacters are now amongst the commonest bacterial causes of diarrhoea in humans. Typically the diarrhoea is very watery, and blood and mucus may be present in the stools. The incubation period is highly variable (few hours through to several days). This variability is correlated with the density of the inoculum of the infecting dose. Infections may be spread by drinking contaminated water or drinking unpasteurised milk, as well as by eating particular foods, especially undercooked chickens.

Clostridium spp.: Toxigenic strains Clostridium perfringens cause a self-limiting diarrhoeal disease. Spores of the bacterium survive initial cooking, and often the subsequent reheating of meat stews, particularly when cooked in large quantities. Clostridium perfringens diarrhoea is most commonly seen in institutional catering, such as schools, hospitals and university halls of residence. The incubation for clostridial food poisoning is longer than for many intoxications, since toxin production relies first upon germination and growth of the bacterium in the gut before sporulation and toxin production occurs. Very rarely, Clostridium perfringens has been associated with a rapidly fatal diarrhoeal illness, from which patients can die in under two days. In general Clostridium difficile infection primarily affects the hospitalised elderly. It is a more common cause of gastrointestinal infection in the elderly that either campylobacter or salmonella infections.

Escherichia coli: Several types of Escherichia coli are associated with diarrhoeal disease. In the scientific and medical literature these may be referred to by a variety of names such as ETEC's (enterotoxigenic E. coli), EPEC's (enteropathogenic E. coli), EAEC's (enteroaggregative E. coli) and EIEC's (enteroinvasive E. coli), etc. Clinical presentations of disease caused by different types of E. coli associated with diarrhoeal disease show considerable overlap. Escherichia coli diarrhoea is most often associated with journeys, and is often referred to as 'Traveller's diarrhoea'. Children under 2 years old are also vulnerable to Escherichia coli diarrhoea, and without prompt rehydration, they may die from their infection. Strains of Escherichia coli that produce a heat-labile toxin (LT) cause a watery diarrhoea. This toxin is genetically closely related to the toxin produced by campylobacters and by Vibrio cholerae, the bacterium that causes cholera. A heat-stable toxin (ST) is produced by strains of Escherichia coli that cause a diarrhoea that is reminiscent of mild bacilliary dysentery. The toxin is genetically similar to the Shiga toxin produced by Shigella dysenteriae. A third toxin, the vero toxin causes cell destruction, and is so named because its cytopathic effects are easily demonstrated using cultured 'vero' cells. Such strains are associated with consumption of undercooked hamburgers or drinking unpasteurised milk.

Vibrio spp.: Cholera is an exclusively human disease, and like typhoid is spread through consumption of contaminated water. For many years this disease was only associated with a single serovar of Vibrio cholerae now referred to as the 'classical' serotype. More recently, a second serovar has been identified that causes a less severe form of the disease. This is the 'El Tor' serotype. The infectious dose is very high, in excess of 100,000,000 bacteria. The disease is caused by the activity of a toxin, 'choleragen'. This causes alterations of levels of intracellular cyclic AMP in intestinal cells, which reverses the cellular sodium pumps and causes an efflux of sodium from the body. This then causes water loss into the lumen of the intestine on a massive scale because of osmotic pressure. Patients die of electrolyte imbalance.

Bacillus cereus: Bacillus cereus is associated with two types of gastrointestinal disease. The first to be recognised was an intoxication, the second is similar to the diarrhoea caused by strains of Clostridium perfringens. Bacillus cereus intoxication is typically associated with the consumption of fried rice the 'Chinese Restaurant Syndrome'. Spores survive the initial boiling of rice that is then allowed to cool in bulk. During the slow cooling, spores germinate and vegetative bacteria multiply, then sporulate again. Sporulation is also associated with toxin production. Within 16 hours of eating contaminated fried rice, patients suffer a bout of vomiting that generally lasts for less than a day.

Listeria monocytogenes: Although it causes systemic infections, particularly in neonates and the immunocompromised, Listeria monocytogenes is spread by the consumption of contaminated foods and dairy products. Because of the ability of this bacterium to grow at low temperatures, concerns have been expressed about the safety of cook-chill foods, where food is cooked than stored refrigerated at temperatures above freezing for up to a week prior to rewarming then consumption.