Salmonella Gastroenteritis

The HPA reported 14,465 cases of all Salmonella in the year 2000 and there has been a downward trend in the subsequent years (provisional figures for 2008 show a total of 9,867 cases).³ The majority of cases are S. enteritidis. The highest rate of infection is in those over 70 and under 20, especially infants. Salmonella infection is a possible cause of traveller's diarrhoea.

S. enteritidis infections are classified as either PT4 or others. The number reported to the HPA for England and Wales for 2000 were 4,719 and 3,549 respectively and provisional figures for 2008 were 912 and 3,278 respectively.⁴ The reduction in PT4 infections is the main reason for the downward trend in total cases and this may relate to poultry vaccination and less importing of eggs from abroad.

• Salmonella are found in a great many animals, domestic, agricultural and wild. Intensive farming methods are thought to be behind its initial rise to importance.
• Contamination occurs from animal faeces, and infected foods usually look and smell normal.
• Many cases arise from outbreaks e.g. weddings.
• The source is usually of animal origin, such as beef, poultry, unpasteurised milk or eggs, but all food, including vegetables may be contaminated.
• Eggs continue to be a source of infection. In 2006, the Foods Standards Agency examined eggs for salmonella and estimated that contamination was present in 1 box out of 30. Of 1,744 boxes sampled, there were positive results from the shells in 157 cases and from within the egg in 10 instances. Spain and France were the commonest source of contaminated eggs but only 10% of eggs used in the UK come from abroad and most of these are used in the catering industry.⁵
• Organisms multiply rapidly in warm humid conditions, and cross contamination between surfaces and tools used in cooked and infected uncooked food areas is a potential source.
• Inadequate thawing from freezing is a common source. Heat readily kills salmonella, but it can survive spit and oven roasting if not properly defrosted.
• Salmonella infection can also be spread by the faeco-oral route if a carrier does not wash hands after using the toilet.
• Gastric acidity gives some protection, and thus large inoculums are required. Conversely those with loss of acidity, including those on acid suppressing drugs, are more at risk. Also liquids which pass through the stomach quickly, or milk and cheese that raise the pH, enable smaller inoculums to be infective.

Symptoms

• Incubation period is 12 to 72 hours.
• Diarrhoea starts with fever and abdominal cramps. The diarrhoea can be bloody. (Note that diarrhoea is not a feature of typhoid fever and constipation is common.)
• The illness tends to last 4 to 7 days and there is recovery.
• Always enquire about recent attendance to social gatherings, anybody else with a similar illness and any recent travel.

Signs

• There is a temperature of 38 to 39°C for about 48 hours.
• There may be signs of dehydration.
• There is not the typical rash of typhoid.

• Campylobacter
• Cryptosporosis
• E coli O157 (can cause bloody diarrhoea)
• Listeria monocytogenes
• Cyclospora
• Shigella
• Yersinia

• Diagnosis is by culturing the organism from the stool.
• FBC will probably show an elevated white cell count but in most cases in primary care, stool culture is the only necessary investigation.
• Agglutination tests such as the Widal test are not recommended as there are often false positives.

Non-drug

• Attention to dehydration, usually just oral rehydration fluids.
• Attention to hand washing to prevent spread to others.
• Admission to hospital may be required in infants younger than 3 months or younger than 12 months with a temperature in excess of 39°C.
• Other indications for admission may include immunosuppression, chronic GI illness and haemoglobinopathies.

Drugs

• Antibiotics do not shorten the illness but may prolong the carrier stage.⁶ There is also a problem of multiple antibiotic resistance.⁷
• They may be used in the severely ill, especially the immuno-compromised.⁸
• Sometimes anti-diarrhoea or anti-spasmodic drugs may be required. Their use is controversial as prolongation of the transit time may prolong the disease.

Return to work

When diarrhoea has settled the vast majority are not a risk to others and may return to work with no further testing. The following need advice from Environmental Health officers or a Consultant in Communicable Disease Control (CCDC):

• Food handlers
• Health-care, nursery or other staff who have direct contact with people who are susceptible to infection
• Children under 5 years attending nurseries, play groups or nursery schools

• Infants, the elderly and those with immunological compromise are more likely to have more severe disease and to require admission to hospital for rehydration.
• Seeding of bacteria outside the gut is rare but raises mortality rates. Sites include endocarditis and arterial infections, cholecystitis, hepatic and splenic abscesses, urinary tract infections (if stones present), pneumonia or empyema, meningitis, septic arthritis, and osteomyelitis.

Mortality is about 0.4% but about 70 times higher in patients from residential homes. Most people recover uneventfully.

• Poultry and meat, including burgers should be well cooked, not pink in the middle. Vegetables and salads should be thoroughly washed before eating. The Chief Medical Officer advises against recipes with uncooked or lightly cooked eggs. Adequate cooking of eggs, until the yolk is set, kills salmonellas. Take care that food does not become contaminated after cooking.
• Uncooked meats kept separate from cooked and ready to eat food to avoid cross contamination.
• Hands, chopping boards, knives and other utensils should be washed thoroughly in hot soapy water immediately after handling raw meat and poultry. Strict separation of surfaces, tools, clothing, and staff for cooked food preparation areas and uncooked food preparation areas must be enforced (contaminated aprons/knives can easily transmit infection between areas).
• Hands should be washed before handling different food items and before eating or drinking and after going to the toilet and also after contact with animals particularly pets and their bedding.
• Those who are ill should not prepare or handle food.
• Carrier states - some people may be asymptomatic carriers of salmonella. This is important especially in those who handle food or work in nurseries and the health profession. The use of quinolone antibiotics in these cases e.g. norfloxacin and ciprofloxacin, have been successful in eradicating carriage of salmonella.⁹