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Suspected food poisoning
Department of Microbiology, Barking, Havering and Redbridge Trust
ST2, Core Medical Training, Department of Medicine, King George Hospital, Barking, Havering and Redbridge Trust
E-mail: markmelzer{at}hotmail.com
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Abstract |
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 TOP Abstract The GP curriculum and...Clinical presentation, history...Food-borne pathogensConclusionReferences |
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Food poisoning is defined as ‘any disease of an infective or toxic nature caused by or thought to be caused by the consumption of food and water’. The term ‘food poisoning’ is, in fact, a misnomer and is more accurately described as ‘food-borne infections and intoxications’ (Collee, 1989) or infectious intestinal diseases (IIDs). Data from 2006, released by the Health Protection Agency for England and Wales, totalled 70 603 cases of food-borne illness and 211 deaths (excluding enterocolitis caused by Clostridium difficile). Cohort studies based in general practice found that, of the 9.4 million estimated cases of IID, only 1.5 million will consult their general practitioner approximating to one in six (Wheeler et al., 1999). With total costs to the economy estimated at £1.5 billion a year, the Food Standards Agency launched a strategic campaign in June 2008 to reduce this prevalence, in particular, the high numbers of cases notified during summer months.
The predominant symptoms of food poisoning are diarrhoea, abdominal pain, nausea and vomiting. These are highlighted in the knowledge base of 15.2: Digestive problems. Elderly patients and those with pre-existing diseases are more likely to suffer significant morbidity and mortality from infectious intestinal diseases (IIDs). This article gives valuable advice to GPs caring for acutely ill patients caused by food poisoning. Considering that general practitioners have an important role in health promotion and disease prevention; this article focuses on advice and methods of prevention and spread of food poisoning highlighted in curriculum statement 5: Healthy people.
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Figure 1 illustrates the total reported cases of food poisoning to the Health Protection Agency (HPA) between 1986 and 2006.
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Clinical presentation, history taking and examination |
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TOPAbstractThe GP curriculum and...Clinical presentation, history...Food-borne pathogensConclusionReferences |
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Diarrhoea, vomiting and abdominal pain, with or without fever, are common presenting symptoms of food poisoning. Given the time constraints in general practice, a targeted history will provide most clues to differentiate the cause and risk stratify patients (Box 1). Important information to elicit includes timing and onset of symptoms, frequency of vomiting and diarrhoea, blood or mucus within the stool, description of stool, presence of fever, arthritis and skin rash. A detailed food history should include recent meals in the preceding 48 hours and specific enquiry into the consumption of seafood, undercooked poultry, canned food, unpasteurized dairy products or raw eggs should be made. Furthermore, one should enquire into shared meals with others suffering similar symptoms and recent foreign travel.
| Box 1. A targeted history Presenting history
Food history
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Physical examination should focus on the degree of dehydration (Box 2). Assessment should include skin turgor, examination of jugular venous pressure, mucous membranes, pulse and lying and standing blood pressure. A febrile patient will have higher insensible losses and therefore, more probably, electrolyte disturbance which can result in altered mental status. Examination of the abdomen will help exclude an acute surgical abdomen. Digital rectal examination may be required to directly examine the stool and for palpation of any rectal mass.
Box 2. A focused examination
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In an attempt to reduce the number of cases, the Food Standards Agency (FSA) has focused on the five major microorganisms that cause food poisoning. These are Campylobacter, Salmonella and Clostridium perfringens, responsible for the greatest number of cases; and Verocytotoxin-producing Escherichia coli (VTEC) O157 and Listeria monocytogenes, which also cause severe disease but are fewer in number. In addition to these organisms, they also describe other toxin-mediated and non-toxin-mediated bacterial infections, viruses and protozoa.
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Food-borne pathogens |
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TOPAbstractThe GP curriculum and...Clinical presentation, history...Food-borne pathogensConclusionReferences |
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Bacterial pathogens (non-toxin mediated)
Campylobacter (Fig. 2) is the commonest reported bacterial cause of IID in England, Wales and worldwide typically causing fever, diarrhoea and abdominal cramps. The infection is often contracted by eating undercooked poultry, unpasteurized milk, untreated water and food that has been contaminated with raw affected meat. About 46 603 laboratory reports of faecal isolates with Campylobacter were reported to the HPA in 2006. In England, it also causes the majority of GP visits and referral to hospital. Two species account for the majority of infections, Campylobacter jejuni and Campylobacter coli. Guillain–Barré syndrome is a well-recognized but rare complication of Campylobacter infection.
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Present in the intestines of many mammals, poultry and reptiles, non-typhi Salmonellae (NTS) are typically contracted from beef, poultry, eggs and dairy products contaminated with the bacterium. Patients may describe an acute onset of watery diarrhoea, sometimes bloody, with a low-grade fever and abdominal cramps. In addition, a reactive arthritis may also be present. Vomiting classically starts 6–48 hours after exposure and may last up to 12 days. Systemic infection, salmonella septicaemia, can be life threatening and those most at risk are immunocompromised patients. In bacteraemic cases, haematogenous spread to atheromatous plaques has been described. Reported cases of Salmonella in humans (excluding Salmonella typhi and Salmonella paratyphi) and Campylobacter from faecal isolates reported to the HPA for Infections in England and Wales between 1981 and 2006 are illustrated in Fig. 3.
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In contrast to NTS, S. typhi and S. paratyphi are non-zoonotic infections, so are not contracted from animals but from heavily infected water that is contaminated with the faeces and urine of other infected humans. Nearly all infections in the UK are acquired abroad, most commonly in the Indian subcontinent. Despite historical textbook descriptions, diarrhoea does occur with these diseases, particularly with S. paratyphi A infections. Notification of this disease is extremely important to prevent secondary cases, particularly among food handlers.
Shigellosis is caused by four species: Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella sonnei. Cases of the former three are often contracted outside the UK and commonly acquired by drinking water contaminated with faeces. Stools are characteristically, but not always, bloody with mucus and a reactive arthritis can also occur. Shigella dysenteriae is associated with serious complications including toxic megacolon and haemolytic uraemic syndrome (HUS) which is discussed later.
Yersinia are Gram-negative rods responsible for food-borne yersiniosis. The causative organism is Yersinia enterocolitica which causes watery diarrhoea, abdominal pain, fever and occasionally an arthritis. Erythema nodosum and pharyngitis have been associated with Yersinia infection. Classically pork and unpasteurized milk have been described as the foods causing infection.
Listeria is a rare but potentially life-threatening disease among the young, elderly, pregnant women and the immunocompromised. In pregnancy, it can result in miscarriage, premature delivery or severe illness in the newborn. Pregnant women should be routinely advised to avoid high-risk food sources from an early stage in the pregnancy. These include unpasteurized cheese, cold meat and pâtés. Listeria monocytogenes can grow at temperatures below 5°C and so can multiply in refrigerated food but can be eradicated by thorough cooking and by pasteurization. An otherwise healthy adult is likely to suffer gastro-enteritis type symptoms but septicaemia and meningitis can occur.
Bacterial pathogens (toxin mediated)
Clostridium perfringens forms part of the normal gut flora and is widely present in food and the environment. The spores of this Gram-positive, rod-shaped bacteria can survive heating to standard cooking temperatures and the bacterium has a doubling time of 10 minutes when food is kept warm for prolonged periods after cooking. Resulting food poisoning typically lasts under 24 hours and its effects are mediated by an enterotoxin produced by the bacterium after ingestion. It is the third most common cause of food poisoning reported to the HPA.
Staphylococcus aureus food poisoning causes symptoms 2–4 hours after ingestion of food that has often been contaminated by food handlers. Clinical features are those common to most other IIDs but it is the rapid onset which is classically associated with staphylococcal food poisoning. These effects occur as a result of enterotoxin produced by this organism in products such as seafood, meat and dairy products stored at room temperature before being consumed cold.
Of the toxin-producing E. coli that cause food poisoning, E. coli O157:H7 is the most important cause of illness in humans. Although relatively rare in England, the disease can be severe causing a haemorrhagic colitis and HUS. HUS, more common in young children, is characterized by acute renal failure, haemolytic anaemia and thrombocytopenia. Adults are more likely to develop thrombotic thrombocytopenic purpura (TTP) when HUS is seen with neurological sequelae. Fatality rates from E. coli 0157 depend on the patients affected and are higher when complicated by HUS or TTP. Reported fatality rates range from 1% to 5% but may be much higher. Other strains of E. coli are also responsible for IIDs. Enterotoxic E. coli is the major cause of traveller's diarrhoea and can lead to profuse diarrhoea lasting several days in people travelling to tropical climates (Fig. 3).
Bacillus species commonly contaminate raw food particularly when in contact with the soil. Preformed toxin and further toxin produced when in the gastro-intestinal tract cause diarrhoea, vomiting, nausea and abdominal pain. Bacillus cereus typically causes nausea and vomiting within 5 hours and diarrhoea in 16 hours. Bacillus subtilis may cause symptoms within 10 minutes and Bacillus licheniformis causes diarrhoea in 2–14 hours.
Clostridium botulinum is a rare cause of food poisoning in the UK and spores are commonly found in soil. Clostridium botulinum produces a neurotoxin leading to Botulism. Clinical presentation is characterized by the four ‘Ds’: diplopia, dysphonia, dysphagia and a descending paralysis. Most cases recover, often after 90 days, but death due to respiratory failure occurs in 5–10% of cases. The last reported fatality from naturally occurring botulism to the HPA was in 2003 due to a home-made sausage imported from Poland. Treatment requires urgent admission to ITU for respiratory support and intravenous antitoxin.
Cholera occurs when food and water become contaminated with the 01 and 0139 strains of the bacterium. Vibrio cholerae causes an acute IID, it has a relatively short incubation period and the enterotoxin rapidly causes large volume, painless, watery diarrhoea, vomiting and myalgia. Approximately one-fifth of patients will develop signs of severe dehydration. It generally occurs in the developing world where there is poorer access to clean water or sewage disposal but has been associated with the consumption of raw oysters in the UK.
Viruses
Viral causes of IID are common causes of gastro-enteritis especially among younger children. Symptoms generally have a shorter duration and require symptomatic treatment only. However, they are a significant cause of morbidity and hospital admissions. Some of the more common viruses are discussed below.
Rotavirus is the most common cause of gastro-enteritis in infants. Approximately 18 000 children are hospitalized each year in England and Wales due to rotavirus and infection normally results in lifelong immunity. The typical symptoms last from 3 to 8 days. Adenoviruses are a common cause of IID in children, particularly strains 40 and 41. Astroviruses mainly affect the under fives and similar to rotavirus, infection in childhood is believed to give long-lasting immunity. The caliciviruses include noroviruses and sapoviruses. Most people affected make a full recovery within a couple of days and rarely require medical attention. Norovirus is the most common cause of infectious gastro-enteritis in England and Wales as immunity is short lived. Outbreaks are common in hospital wards, nursing homes, cruise ships and schools where prevention of spread requires meticulous attention to hygiene, cleanliness and separation of symptomatic patients.
Protozoa
Giardia is an important cause of food poisoning and gastro-enteritis to consider in those with a recent history of travel. It can be transmitted by direct contact and by ingestion of food stuffs contaminated by the faeces of infected individuals. The incubation period is widely variable, 5–25 days. In addition to the typical symptoms, bloating and mildly bloody stools should raise the suspicion of Giardia lamblia infection. Non-invasive diagnosis is made by the detection of cysts in the stool (Fig. 5).
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Cryptosporidiosis, caused by Cryptosporidia parvum, is most common in children from 1 to 5 years of age. Exposure to cattle (e.g. petting at animal farms) and exposure from contaminated swimming pools are potential risks for infection. Recovery can be slow and treatment is symptomatic but symptoms can persist for up to a month. Infection is frequently associated with foreign travel and consumption of food contaminated with infected faeces. Immunocompromised patients are at particular risk of severe infection. Entamoeba histolytica is another parasitic infection that may cause a stool mixed with blood and mucus, in those recently returned from Africa or the Indian subcontinent.
Diagnosis
As many diarrhoeal illnesses are short lived and many are viral, microbiological investigation to culture a non-viral pathogen is not usually warrented when patients present within 24 hours after onset unless they are dehydrated, febrile or have pus or blood in the stool (Thielman, 2001). Initial investigations in general practice include culture of stool and sensitivity testing. If febrile, blood cultures should also be ascertained where possible. Food, where a causative meal or ingredient is strongly suspected, should be obtained and sent for processing at a reference laboratory. Microscopic examination of the stool for ova, cysts and parasites should be specifically requested for patients with a recent travel history where diarrhoea persists for more than 10 days. In patients known to be HIV seropositive, special stains for microsporidia and cryptosporidia should also be requested.
Treatment
Adequate rehydration and replacement of electrolytes is of primary concern. Options to achieve this include preparations of oral rehydration solution recommended by the World Health Organization (WHO). These are glucose-based electrolyte solutions available over the counter in the developed world. In the developing world, they are supplied by UNICEF and WHO as mixtures of specific quantities of essential electrolytes and glucose to be diluted in water. The physiological benefit of such solution is based around the sodium glucose transporters which increase water absorption along the gastro-intestinal tract. They have undoubtedly saved millions of lives worldwide. In severely dehydrated patients, this may be inadequate and inpatient admission may be necessary where intravenous rehydration is warranted. Patients may acquire transient lactose intolerance so, for adult patients, avoiding milk and dairy products during the acute illness are advised. However, among children, data on the avoidance of dairy products are limited.
Antimicrobials for food poisoning are the subject of much debate. In a randomized control study of 173 patients, Dryden et al. recruited patients with more than four fluid stools a day for more than three days and 81 were treated with either ciprofloxacin 500 mg twice daily or placebo for 5 days. The authors observed a reduction in diarrhoea and other symptoms after 2 days, with fewer treatment failures, and significantly greater clearing of pathogens when compared with placebo. In a literature review published in a British Medical Journal editorial in 1997, Gorbach concluded that adults with severe community-acquired diarrhoea, defined as more than four loose motions a day and an associated symptom, should receive an antimicrobial drug, preferably a fluoroquinolone.
In immunocompetent patients found to have Campylobacter infection, erythromycin reduces bacterial carriage but only reduces duration of illness when commenced within four days of onset of symptoms. The immunocompromised are at higher risk of complications from Campylobacter and those with prolonged symptoms may benefit from antimicrobials. Uncomplicated salmonella infection does not usually warrant antibiotics as they do not typically improve symptoms. However, high-risk patients, including those who are pregnant or immunocompromised (for example, those who are seropositive for HIV) and those who suffer from haemoglobinopathies, severe atherosclerosis, degenerative arthritis and valvular heart disease are all at increased risk of severe infection and warrant antibiotics. If an antibiotic is to be prescribed, a stool sample must first be collected and sent to the microbiology laboratory.
With regards to travellers’ diarrhoea, most trials have indicated that antibiotics taken as a single dose or for up to 3 days will improve the condition within 20–36 hours (Hill, 2008). A short course of treatment is usually well tolerated and adverse events mild. However, potential complications include anaphylaxis, allergy, antibiotic resistance and Clostridium difficile enterocolitis. Fluoroquinolones are considered effective for cases where resistant Campylobacter is not common; however, patients travelling to South Asia and South East Asia may encounter resistance and so azithromycin is recommended in such cases (Hill, 2008).
Given that the majority of cases in children are viral in aetiology, the authors strongly advise careful consideration when considering empirical antibiotic treatment in children. If antibiotics are required, we recommend consulting local microbiology and infectious diseases guidelines and policies.
Prevention and notification
The HPA and FSA provide excellent information for the public on prevention of food poisoning. They suggest that by addressing the ‘four Cs’; cleaning, cooking, chilling and cross contamination and that following advice on basic hygiene, food preparation and storage, domestic food poisoning can be prevented. This advice should be reiterated to patients given that a recent FSA survey showed that three-quarters of the public had never heard of the most common cause of food poisoning, 82% of people believe they are unlikely to get food poisoning from food at home, 89 percent do not store raw meat properly and 63 per cent do not wash their hands after handling raw meat or fish.
Section 11 of the Public Health (Control of Disease) Act 1984 requires a registered medical practitioner attending anyone who he/she has reason to suspect may be suffering from one of a list of conditions to notify forthwith the Proper Officer for the Local Authority (local council) of that district. Food poisoning is legally notifiable and not the specific organism itself. Notification is essential to track cases, contain spread and record epidemiological data. Microbiology laboratories routinely send all Salmonella species, isolated from stool, to a reference laboratory so that organisms can be typed for epidemiological purposes.
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Conclusion |
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TOPAbstractThe GP curriculum and...Clinical presentation, history...Food-borne pathogensConclusionReferences |
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Food poisoning is an important cause of diarrhoea and vomiting resulting in days off work and admissions to hospital. In vulnerable patient groups, such as children, the elderly and immunocompromised, it is a significant cause of morbidity and even mortality. With basic knowledge of hygienic food preparation and storage, many cases can be prevented. Although many cases will be managed in the community, it is important to understand that maintaining adequate hydration is the mainstay of treatment and antibiotic therapy is only indicated in certain circumstances. Notification is mandatory so that further cases caused by cross-contamination can be prevented.
Key points
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References |
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