Infectious causes of acute gastroenteritis are listed in Box 5.4.
Staphylococcal food poisoning
S. aureus transmission occurs from the hands of food handlers to food- stuffs such as dairy products, including cheese, and cooked meats.
Inappropriate storage permits growth and production of heat- stable enterotoxins.
Nausea and vomiting develop within 1 to 6 hours. Diarrhoea may not be marked. Most cases settle rapidly, but severe dehydration can occasionally be life- threatening. Antiemetics and fluid replacement are the mainstays of treat- ment. Public health authorities should be notified if food vending is involved.
Bacillus cereus
Ingestion of the preformed enterotoxins of B. cereus leads to rapid onset of vomiting and some diarrhoea within hours of food consumption, resolving within 24 hours. Fried rice and sauces are frequent sources; enterotoxin is formed during storage.
If viable organisms are ingested, the toxin is produced within the gut, leading to a longer incubation period of 12 to 24 hours and watery diar- rhoea with abdominal cramps. The disease is self- limiting. Management consists of fluid replacement and public health notification.
Clostridium perfringens
Spores of C. perfringens are widespread in the guts of large animals and in soil. If contaminated meat products are incompletely cooked and stored in anaerobic conditions, C. perfringens spores germinate, and viable organ- isms multiply. Subsequent reheating of the food causes release of entero- toxin. Symptoms (diarrhoea and cramps) occur 6 to 12 hours following ingestion. The illness is usually self- limiting.
Clostridial enterotoxins are potent, and most people who ingest them will be symptomatic. ‘Point source’ outbreaks, in which a number of cases all become symptomatic following ingestion, classically occur after school or canteen lunches where meat stews are served.
Campylobacter jejuni
This infection is a zoonosis, although the organism can also survive in fresh water. It is the most common cause of bacterial gastroenteritis in the UK.
The usual sources are chicken, beef or contaminated milk products, but contact with pet puppies has also caused cases.
The incubation period is 2 to 5 days. Colicky abdominal pain develops along with nausea, vomiting and significant diarrhoea, frequently containing blood. Most Campylobacter infections affect fit young adults and are self- limiting after 5 to 7 days. Some 10% to 20% have prolonged symptoms and merit treatment with a macrolide, usually azithromycin, as ciprofloxacin resistance is common. About 1% of cases will develop bacteraemia and possible distant foci of infection. Campylobacter spp. have been linked to Guillain- Barré syndrome and postinfectious reactive arthritis.
Salmonella spp.
Salmonella enterica serovars other than Salmonella Typhi and Paratyphi (p. 135) are widely distributed in animals and can cause gastroenteritis.
Worldwide, the most important are Salmonella Enteritidis phage type 4 and Salmonella Typhimurium DT104. The latter may be resistant to ciprofloxa- cin. Transmission is by contaminated water or food, particularly poultry, egg products and minced beef; person- to- person spread; or from exotic pets, for example, salamanders, lizards or turtles.
The incubation period of Salmonella gastroenteritis is 12 to 72 hours, and the predominant feature is diarrhoea, sometimes containing blood. Vomit- ing may be present at the outset. About 5% of cases will be bacteraemic.
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Infection is introduced through insect bites or by contact with infected animals. The most common ‘ulceroglandular’ variety of the disease (70%–80%) is characterised by skin ulceration with regional lymphade- nopathy. Inhalation of the infected aerosols may result in pulmonary tul- araemia, presenting as pneumonia. Rarely, the portal of entry of infection may be the conjunctiva, leading to a nodular, ulcerated conjunctivitis with regional lymphadenopathy (an ‘oculoglandular’ form). Demonstration of a single high titre (≥1:160) or a fourfold rise in 2 to 3 weeks in the tularaemia tube agglutination test confirms the diagnosis. DNA detection methods to enable rapid diagnosis are in development. Treatment consists of 10 to 21 days of parenteral streptomycin or gentamicin, or oral doxycycline or ciprofloxacin.
Melioidosis
Melioidosis is caused by Burkholderia pseudomallei, and is common in South- East Asia and Australia. Inhalation or inoculation leads to bacter- aemia with pneumonia and abscesses in the lungs, liver, spleen and sub- cutaneous tissues. The CXR may resemble cavitary TB. Culture of blood, sputum or pus may yield B. psuedomallei. Treatment is with IV ceftazidime or meropenem, followed by oral co- trimoxazole or doxycycline for 3 to 6 months. Abscesses should be drained.
Actinomycete infections Nocardiosis
This uncommon infection is caused by aerobic actinomycetes (genus Nocardia), found in soil. Traumatic inoculation, inhalation or ingestion causes cutaneous ulcers or nodules, usually on the legs. In tropical coun- tries, chronic infection can develop into actinomycetoma, involving soft tissues and occasionally bone (p. 171). In immunocompromised individu- als, systemic Nocardia causes suppurative disease with lung and brain abscesses. Treatment of systemic infection requires imipenem with ceftri- axone, amikacin or co- trimoxazole, for 6 to 12 months or longer.
Actinomyces spp.
Actinomyces are anaerobic actinomycetes, oral commensals which can cause deep, suppurating infection in the head and neck, the lungs and the pelvis (associated with IUCDs). The most common species is Actinomyces israelii. Treatment requires prolonged penicillin or doxycycline.
Gastrointestinal bacterial infections
Food PoisoningInfectious causes of acute gastroenteritis are listed in Box 5.4.
Staphylococcal food poisoning
S. aureus transmission occurs from the hands of food handlers to food- stuffs such as dairy products, including cheese, and cooked meats.
Inappropriate storage permits growth and production of heat- stable enterotoxins.
Nausea and vomiting develop within 1 to 6 hours. Diarrhoea may not be marked. Most cases settle rapidly, but severe dehydration can occasionally be life- threatening. Antiemetics and fluid replacement are the mainstays of treat- ment. Public health authorities should be notified if food vending is involved.
Bacillus cereus
Ingestion of the preformed enterotoxins of B. cereus leads to rapid onset of vomiting and some diarrhoea within hours of food consumption, resolving within 24 hours. Fried rice and sauces are frequent sources; enterotoxin is formed during storage.
If viable organisms are ingested, the toxin is produced within the gut, leading to a longer incubation period of 12 to 24 hours and watery diar- rhoea with abdominal cramps. The disease is self- limiting. Management consists of fluid replacement and public health notification.
Clostridium perfringens
Spores of C. perfringens are widespread in the guts of large animals and in soil. If contaminated meat products are incompletely cooked and stored in anaerobic conditions, C. perfringens spores germinate, and viable organ- isms multiply. Subsequent reheating of the food causes release of entero- toxin. Symptoms (diarrhoea and cramps) occur 6 to 12 hours following ingestion. The illness is usually self- limiting.
Clostridial enterotoxins are potent, and most people who ingest them will be symptomatic. ‘Point source’ outbreaks, in which a number of cases all become symptomatic following ingestion, classically occur after school or canteen lunches where meat stews are served.
Campylobacter jejuni
This infection is a zoonosis, although the organism can also survive in fresh water. It is the most common cause of bacterial gastroenteritis in the UK.
The usual sources are chicken, beef or contaminated milk products, but contact with pet puppies has also caused cases.
The incubation period is 2 to 5 days. Colicky abdominal pain develops along with nausea, vomiting and significant diarrhoea, frequently containing blood. Most Campylobacter infections affect fit young adults and are self- limiting after 5 to 7 days. Some 10% to 20% have prolonged symptoms and merit treatment with a macrolide, usually azithromycin, as ciprofloxacin resistance is common. About 1% of cases will develop bacteraemia and possible distant foci of infection. Campylobacter spp. have been linked to Guillain- Barré syndrome and postinfectious reactive arthritis.
Salmonella spp.
Salmonella enterica serovars other than Salmonella Typhi and Paratyphi (p. 135) are widely distributed in animals and can cause gastroenteritis.
Worldwide, the most important are Salmonella Enteritidis phage type 4 and Salmonella Typhimurium DT104. The latter may be resistant to ciprofloxa- cin. Transmission is by contaminated water or food, particularly poultry, egg products and minced beef; person- to- person spread; or from exotic pets, for example, salamanders, lizards or turtles.
The incubation period of Salmonella gastroenteritis is 12 to 72 hours, and the predominant feature is diarrhoea, sometimes containing blood. Vomit- ing may be present at the outset. About 5% of cases will be bacteraemic.
Reactive (postinfective) arthritis occurs in about 2% of cases. Antibiotics are not indicated unless there is bacteraemia, which is a clear indication for antibiotic therapy, as salmonellae are notorious for persistent infection and often colonise endothelial surfaces such as an atherosclerotic aorta or a major blood vessel.
Escherichia coli
Many serotypes of E. coli exist in the human gut microbiome. Clinical disease requires either colonisation with a new strain or acquisition by a colonising strain of a new pathogenicity factor (e.g. toxin production). There are five dif- ferent clinico- pathological patterns of disease, all associated with diarrhoea.
Enterotoxigenic E. coli (ETEC): This is the most common among the many causes of travellers’ diarrhoea in developing countries (Box 5.16).
The organisms produce either a heat- labile or a heat- stable enterotoxin, causing marked secretory diarrhoea and vomiting after 1 to 2 days’ incuba- tion. The illness is usually mild and self- limiting after 3 to 4 days. Antibiotics are of questionable value.
Enteroinvasive E. coli (EIEC): This illness is very similar to Shigella dysentery and is caused by invasion and destruction of colonic mucosal cells. No enterotoxin is produced. Acute watery diarrhoea, abdominal cramps and some scanty blood- staining of the stool are common. The symptoms are rarely severe and are usually self- limiting.
Enteropathogenic E. coli (EPEC): These are very important in infant diarrhoea. Ability to attach to the gut mucosa is the basis of their pathoge- nicity. This causes destruction of microvilli and disruption of normal absorp- tive capacity. The symptoms vary from mild, nonbloody diarrhoea to quite severe illness.
Enteroaggregative E. coli (EAEC): These strains adhere to the mucosa and produce a locally active enterotoxin. A ‘stacked brick’ aggregation is seen in the small bowel. They have been associated with prolonged diar- rhoea in children in South America, South- East Asia and India.
Enterohaemorrhagic E. coli (EHEC): A number of distinct ‘O’ sero- types of E. coli produce two distinct enterotoxins (verocytotoxin), which are identical to toxins produced by Shigella (shigatoxins 1 and 2). E. coli O157:H7 is perhaps the best known of these verocytotoxigenic E. coli, but others, including types O126 and O11, are also implicated. The organism has an extremely low infecting dose (10–100 organisms). The reservoir is in the gut of herbivores.
Contaminated vegetables, milk and meat products (especially under- cooked hamburgers) are all recognised sources. The incubation period is between 1 and 7 days. Initial watery diarrhoea becomes uniformly blood- stained in 70% of cases and is associated with severe abdominal pain.
There is little systemic upset, vomiting or fever. Enterotoxins have both a local effect on the bowel and distant effects on the glomerular apparatus, heart and brain. The potentially life- threatening HUS occurs in 10% to 15%
of cases, arising 5 to 7 days after the onset of symptoms. It is most likely at the extremes of age, is heralded by a high peripheral leucocyte count and may be induced, particularly in children, by antibiotics. HUS is treated by dialysis if necessary, and may be averted by plasma exchange.
Clostridium difficile infection
C. difficile is occasionally present in the gut microbiome and is the most commonly diagnosed cause of antibiotic- associated diarrhoea. Clinical infection usually follows up to 6 weeks after antibiotic therapy, which alters gut flora. Transmission is by spores, which are resistant to alcohol hand gels, and disease results from the production of two toxins. A number of different ribotypes of the organism exist, with the 027 ribotype producing particularly severe disease and significant mortality.
Infection causes diarrhoea, which may be bloody and may be complicated by pseudomembranous colitis. Around 80% of patients over 65 years of age, and many have multiple comorbidities.
C. difficile is found in the stool in 30% of cases of antibiotic- associated diarrhoea and 90% of those with pseudomembranous colitis, but also in 20% of healthy elderly patients in care. Diagnosis therefore depends on finding C. difficile toxin in the stool.
Precipitating antibiotics should be stopped. Treatment is with IV rehydra- tion and oral metronidazole for 10 days or, in severe cases, oral vancomy- cin. Faecal transplantation is used increasingly as a treatment for relapses.
Yersinia enterocolitica
This organism, commonly found in pork, causes mild to moderate gastro- enteritis and can produce significant mesenteric adenitis after an incuba- tion period of 3 to 7 days. It predominantly causes disease in children, but adults may also be affected. The illness resolves slowly. Complications include reactive arthritis (10%–13% of cases) and anterior uveitis.
Cholera
Cholera, caused by Vibrio cholerae serotype O1, is the archetypal toxin- mediated bacterial cause of acute watery diarrhoea, and has caused numerous pandemics worldwide. Infection spreads via the stools or vomit of symptomatic patients or of the much larger number of subclinical cases.
The microorganism survives for up to 2 weeks in fresh water and 8 weeks in salt water. Transmission is normally through infected drinking water, shell- fish and food contaminated by flies, or on the hands of carriers.
Clinical features
Severe diarrhoea without pain or colic begins suddenly, followed by vomit- ing. Following the evacuation of normal gut faecal contents, typical ‘rice- water’ material is passed, consisting of clear fluid with flecks of mucus, 5.16 Most common causes of travellers’ diarrhoea
• ETEC • Shigella spp.
• Campylobacter jejuni • Salmonella spp.
• Plesiomonas shigelloides • Noncholera Vibrio spp.
• Aeromonas spp.
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Contaminated vegetables, milk and meat products (especially under- cooked hamburgers) are all recognised sources. The incubation period is between 1 and 7 days. Initial watery diarrhoea becomes uniformly blood- stained in 70% of cases and is associated with severe abdominal pain.
There is little systemic upset, vomiting or fever. Enterotoxins have both a local effect on the bowel and distant effects on the glomerular apparatus, heart and brain. The potentially life- threatening HUS occurs in 10% to 15%
of cases, arising 5 to 7 days after the onset of symptoms. It is most likely at the extremes of age, is heralded by a high peripheral leucocyte count and may be induced, particularly in children, by antibiotics. HUS is treated by dialysis if necessary, and may be averted by plasma exchange.
Clostridium difficile infection
C. difficile is occasionally present in the gut microbiome and is the most commonly diagnosed cause of antibiotic- associated diarrhoea. Clinical infection usually follows up to 6 weeks after antibiotic therapy, which alters gut flora. Transmission is by spores, which are resistant to alcohol hand gels, and disease results from the production of two toxins. A number of different ribotypes of the organism exist, with the 027 ribotype producing particularly severe disease and significant mortality.
Infection causes diarrhoea, which may be bloody and may be complicated by pseudomembranous colitis. Around 80% of patients over 65 years of age, and many have multiple comorbidities.
C. difficile is found in the stool in 30% of cases of antibiotic- associated diarrhoea and 90% of those with pseudomembranous colitis, but also in 20% of healthy elderly patients in care. Diagnosis therefore depends on finding C. difficile toxin in the stool.
Precipitating antibiotics should be stopped. Treatment is with IV rehydra- tion and oral metronidazole for 10 days or, in severe cases, oral vancomy- cin. Faecal transplantation is used increasingly as a treatment for relapses.
Yersinia enterocolitica
This organism, commonly found in pork, causes mild to moderate gastro- enteritis and can produce significant mesenteric adenitis after an incuba- tion period of 3 to 7 days. It predominantly causes disease in children, but adults may also be affected. The illness resolves slowly. Complications include reactive arthritis (10%–13% of cases) and anterior uveitis.
Cholera
Cholera, caused by Vibrio cholerae serotype O1, is the archetypal toxin- mediated bacterial cause of acute watery diarrhoea, and has caused numerous pandemics worldwide. Infection spreads via the stools or vomit of symptomatic patients or of the much larger number of subclinical cases.
The microorganism survives for up to 2 weeks in fresh water and 8 weeks in salt water. Transmission is normally through infected drinking water, shell- fish and food contaminated by flies, or on the hands of carriers.
Clinical features
Severe diarrhoea without pain or colic begins suddenly, followed by vomit- ing. Following the evacuation of normal gut faecal contents, typical ‘rice- water’ material is passed, consisting of clear fluid with flecks of mucus,
resulting in enormous loss of fluid and electrolytes. Shock and oliguria ensue, necessitating fluid and electrolyte replacement.
Investigations and management
The diagnosis should be confirmed by visualisation of the organism on stool dark- field microscopy, which shows the ‘shooting star’ motility of V. cholerae. Rectal swab or stool cultures allow identification. Cholera is notifiable under international health regulations. Replacement of fluid and electrolyte losses is paramount. IV Ringer’s lactate solution is used until vomiting stops; thereafter, oral rehydration solution is used. Up to 50 L may be needed in 2 to 5 days. Treatment with tetracycline, doxycycline or cipro- floxacin reduces the duration of excretion of Vibrio. Strict personal hygiene, a clean piped water supply and good food hygiene practices prevent the spread of disease.
Vibrio parahaemolyticus
This marine organism produces a disease similar to ETEC. It is very com- mon where ingestion of raw seafood is widespread (e.g. Japan). After an incubation period of around 20 hours, explosive diarrhoea, abdominal cramps and vomiting occur. Systemic symptoms of headache and fever are frequent, but the illness is self- limiting, taking 4 to 7 days to resolve.
Bacillary dysentery (shigellosis)
Shigellae are Gram- negative rods, closely related to E. coli, that invade the colonic mucosa. They are often multi- resistant to antibiotics. The organism only infects humans, and its spread is facilitated by its low infecting dose of around 10 organisms. Transmission is most commonly by unwashed hands after defecation. Outbreaks occur in psychiatric hospitals, residential schools and other closed institutions. It is a common accompaniment of war and natural catastrophe.
Disease severity varies with serotype; cases caused by Shigella sonnei are mild, whereas those attributed to S. dysenteriae may be fulminating and cause death within 48 hours. Symptoms include diarrhoea, which may be bloody, colicky abdominal pain and tenesmus. Reactive arthritis or iritis may occasionally complicate bacillary dysentery (p. 620).
Oral rehydration therapy is necessary to replace water and electrolytes.
Antibiotic therapy with ciprofloxacin (500 mg twice daily for 3 days) is effec- tive; azithromycin and ceftriaxone are alternatives. Resistance to all three occurs. Hand- washing is very important.