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Information

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EBMG

Food Poisoning

Essentials

  • Treatment of patients is symptomatic if the causative agent is unknown, with the exception of symptoms suggestive of botulism. Consider the need of therapy again when the cause of food poisoning is known.
  • The aim is to stop an epidemic and to disclose the cause.
    • Nucleic acid detection test for faecal pathogens from a stool specimen should be taken from both symptomatic and asymptomatic individuals, and from close contacts of the index case.
    • In the case of a foodborne epidemic the faecal specimens should be examined for Salmonella, Shigella, Campylobacter, Yersinia, E.coli strains having the ability to cause diarrhoea (including EHEC, EAEC, EIEC, ETEC and EPEC), Clostridium perfringens, Staphylococcus aureus and Bacillus cereus.
    • It is possible to test for viral infections by nucleic acid detection technologies, e.g. norovirus test.
    • In a suspected water-borne epidemic or an epidemic involving a large group of people in an event/meeting, it is worthwhile to test only a subset of involved people, and to discuss the appropriate use of resources with the clinical microbiologist of the local investigating laboratory.
    • A specimen of the suspected food item should be taken.

Definition

  • Food poisoning is caused by bacteria, bacterial toxin(s), or viruses. Symptoms appear abruptly soon after eating contaminated food, generally within 24 hours from exposure. In cases involving Salmonella and Campylobacter the incubation period may be longer.

Aetiology and symptoms

  • Common causes of food poisoning include:
    • bacteria: Clostridium perfringens, Bacillus cereus, Staphylococcus aureus, Salmonella and Campylobacter
    • viruses: norovirus which is the most common causative agent in food- or water-borne epidemics, rotavirus, adenovirus, astrovirus.
  • The number of EHEC infections is on the rise, which may partly be explained by the increase of tests that are based on nucleic acid detection. EHEC outbreaks also influence the number of cases.
  • Food poisoning from abroad is often caused by E. coli (EAEC, EPEC, ETEC).
    • There is geographical variation in the causative agents of food poisoning.
  • For symptoms of the most common types of food poisoning caused by bacteria, see table T1.

Botulism

  • Very rare but severe poisoning caused by the soil bacterium Clostridium botulinum
  • The possible sources of botulism acquired by food poisoning include homemade preserved meat and fish foods, vegetables, meat and meat products, fish and fish products, even pasteurized carrot juice.
  • Symptom that include tiredness, dizziness and dryness of the mouth begin within 12-36 hours of ingesting the toxin. At the same time or within 3 days neurological symptoms develop: visual symptoms, difficulty in swallowing and rapidly progressing muscle weakness.
  • Dust and honey have been identified as possible sources of infant botulism. The infection produces toxins in the gastrointestinal tract.
  • Symptoms affecting the GI tract are absent.
  • Differential diagnosis includes polyradiculitis Guillain-Barré Syndrome (Polyradiculitis), polio Poliomyelitis and Post-Polio Syndrome, encephalitis Encephalitis and myasthenia gravis Myasthenia Gravis.
  • Although the disease is rare, it is important to know and identify as early treatment (antitoxin, assisted respiration) may save the patient's life.

Symptoms of food poisonings caused by common bacteria

Staphylococcus aureusClostridium perfringensBacillus cereusSalmonella
OnsetAbruptAbruptAbruptUsually abrupt
Incubation time3-4 (1-6) h10-12 (-20) h8-16 h6-72 h
VomitingAlmost alwaysSeldomSeldomOften
DiarrhoeaHeavyHeavyHeavyCommon
Abdominal painModerateSevereSevereModerate
FeverNot regularlyNot commonNot commonCommon
Sense of illnessSevere, abruptMildMildCommon
Pain in jointsNoNoNoMay occur
Symptoms last5-12 h6-24 h6-24 hOften 3-5 days, can get prolonged.

History

  • Exact time of the onset of symptoms.
  • Description of the symptoms: diarrhoea, vomiting, fever, sense of sickness, aches.
  • Travel history: staying abroad within recent weeks.
  • History of meals within 24 hours.
    • Foods consumed; who prepared them?
    • Eating places?
    • Who else and how many have eaten the same food?
    • How many are sick?
    • Which food item does the patient suspect?
  • Does the patient's work involve a risk of spreading Salmonella?
    • The handling of unpackaged foodstuffs to be served unheated
    • On a milk production farm, on milk processing tasks other than milking if the farm delivers milk to a dairy where the milk is not pasteurised
  • Severity of food poisoning in relation to age (newborns and the elderly are vulnerable) and to the patient's chronic diseases.

Treatment

  • Sufficient amounts of fluid, at least one third similar to oral rehydration fluid Diarrhoeal Diseases Caused by Microbes
  • Rest; if necessary sickness absence for 1-2 days
  • As necessary, symptomatic treatment of diarrhoea
  • No antimicrobial drug treatment before stool specimen
  • Consideration of antimicrobial therapy
    • EAEC, EPEC, ETEC and enteric salmonellae usually heal spontaneously and antimicrobial therapy is not necessary. Asymptomatic or mild shigella disease is not treated with antimicrobials either. However, if the patient's condition requires antimicrobial therapy or it is justified e.g. because of age or underlying disease, ciprofloxacin (500 mg twice daily, treatment duration 1-3 days) or azithromycin (500 mg once daily, treatment duration 3 days) is recommended.
    • In an EHEC infection, antimicrobial therapy is not recommended due to the risk of haemolytic-uremic syndrome.
    • Campylobacter: if symptoms have eased after the aetiology has been established, antimicrobial therapy is not needed. A symptomatic patient is primarily treated with azithromycin 500 mg once daily, treatment duration 3 days). Fluoroquinolone resistance is common in strains brought from abroad.
  • Advice about toilet hygiene: After defecation and always before touching foodstuffs the hands should be washed with warm water and soap. Hands should be dried with disposable paper napkins, which are used for as long as diarrhoea or the presence of a possible causative agent continues. Norovirus excretion continues for about one month.
  • The patient must avoid preparing meals for other persons.
  • Those whose work entails specific risks for transmitting infections may return to work after two symptom-free days, unless salmonella, shigella or EHEC has been detected in stool culture. Carriers of these microbes must not return to work until their test results are negative.

To clear up the cause of an epidemic

  • Local instructions regarding how epidemics should be investigated may be available through relevant authorities. Find out about these.
  • When a larger group of people have fallen ill or there is a suspicion of an epidemic, the head of local primary care services or the officer in charge of communicable diseases should be immediately contacted (also out of hours). The medical officer in charge evaluates the situation and is responsible for appropriate notification of the authorities in order to further the investigations and to prevent the spreading of the epidemic. In practice, the public health inspector usually takes the food or water samples, and the patient samples are taken at the primary health care clinic.
  • If the infection is suspected to have originated in a public eating place, a take-away or a grocery, the medical officer in charge contacts the place.
  • The history of the patients may often give a clue as regards a particular microbe or foodstuff. Common infectious vehicles are foodstuffs that contain animal protein and are served cold:
    • poorly heated or frozen meat or fish
    • cut cold meat, chicken
    • oysters
    • bean sprouts, salads, sauces and frozen berries
    • eggs and mayonnaise
    • milk products, confectionery
    • holiday-imported meat, meat products and cheese
  • These and raw materials for the meals should be sampled for bacteriological and/or virological examinations.
  • In addition to foodstuffs the inspection should include food-handlers and utensils.
    • Hands: wounds, cutaneous eruptions; specimens of infections
    • Possible symptoms: food-handlers with symptoms should be taken off work if spreading of infection is likely.
    • Utensils: knives, cutting boards, towels, food machinery etc.
  • Faecal specimens should be taken from at least a few persons who are suffering from diarrhoea.

Notification of the authorities

  • Notification of the authorities should be made in suspected and confirmed food-related epidemics in accordance with the local regulations. Certain food poisonings may need to be reported even if encountered as single cases.