Young children are most commonly affected and outbreaks of Shigella gastroenteritis may occur in childcare settings and schools. Travellers are also a commonly affected group. Foodborne outbreaks can occur, with raw vegetables most commonly implicated as the bacterial vector. Sexually transmitted Shigella may occur via the faecal-oral route, especially in men who have sex with men (MSM).
Shigella is a gram-negative, nonmotile, facultatively anaerobic rod.
It has 4 serotypes:
- Serotype A
- Shigella dysenteriae
- Serotype B
- Shigella flexneri
- Serotype C
- Shigella boydii
- Serotype D
- Shigella soneii
- Developed countries:
- Developing countries:
Shigellae are remarkably infectious enteric pathogens that can cause disease after the ingestion of as few as 10 organisms. This virulence is likely due to the acid-resistant nature of the bacterium (through the formation of a biofilm) and the efficient invasion of colonic epithelium.
Once ingested, Shigella may cause an inflammatory reaction in the large intestine through direct invasion of epithelial cells and production of enterotoxins 1 and 2. These enterotoxins increase the chloride permeability of the apical membrane of intestinal mucosal cells. This leads to an influx of chloride and water into the intestine and development of a secretory diarrhoea within a few hours of ingesting Shigella.
Shigella dysenteriae may produce the Shiga toxin which is associated with haemolytic uraemic syndrome. The Shiga toxin targets the endothelium of intestinal blood vessels, inhibiting cell protein synthesis and causing haemorrhage through cell breakdown.
- Abdominal pain - 80%
- Mucoid diarrhoea - 80%
- Bloody diarrhoea - 45%
- Watery diarrhoea - 35%
- Fever - 35%
- Vomiting - 35%
Some individuals may be asymptomatic.
On average, the incubation period is 3 days, with a range of 1-7 days.
Patients initially experience constitutional symptoms such as fever and malaise. Diarrhoea tends to be watery at first, but subsequently may contain blood and mucus.
Symptoms typically last five to seven days and it may take several months before bowel habits return entirely to normal.
- Stool culture
- This is the preferred method for the diagnosis, as it provides an isolate for subsequent susceptibility testing. The stool sample requires prompt handling and optimally should be inoculated onto agar at the bedside. The sensitivity of the culture is is operator dependent and has a sensitivity of about 50%.
It is often difficult to identify the causative organism based on symptoms alone. The bacteria listed can all cause fever, bloody diarrhoea, and abdominal pain. A dietary history may indicate the causative organism, but a stool culture is necessary for a definitive diagnosis.
- Associated with the consumption of undercooked chicken and pork, contaminated water, unpasteurised milk and through contact with infected domestic or farm animals.
- Associated with the consumption of raw or undercooked meat, eggs or egg products.
- Associated with the consumption of undercooked pork.
- Enteroinvasive Escherichia coli
- Associated with the consumption of raw or undercooked meat or deficiently pasteurised dairy products.
- Clostridium difficile
- A history of antibiotic use may be present.
- Inflammatory bowel disease
- Although the symptoms of IBD are similar to that of shigellosis, the clinical features tend to be more chronic in nature and are associated with more significant weight loss. A family history of IBD increases the likelihood of this diagnosis.
General principles of management include rehydration, nutritional support, and antibiotic therapy.
- Supportive therapy
- Hydration is important to compensate for fluid loss from the gastrointestinal tract; oral rehydration is sufficient in most cases.
- Continued feeding is recommended, particularly in young children, to improve recovery.
- Antibacterial therapy
- British Medical Journal (BMJ) best practice guidelines for shigellosis, last updated in 2018, recommend antibiotic therapy for malnourished, immunocompromised or elderly patients. Food handlers and healthcare workers should also be treated. Furthermore, all individuals with severe disease, defined as bloody diarrhoea with cramping while systemically unwell, should be given antibiotics.
- The British National Formulary (BNF) recommends ciprofloxacin as the antibiotic of choice.
- Preventive therapy
- The spread of Shigella can be stopped by frequent and careful handwashing with soap and taking other hygiene measures.
- These are uncommon and include toxic megacolon, rectal prolapse, intestinal obstruction and colonic perforation.
- Dehydration - 50%
- Metabolic disturbances
- Hyponatremia may occur due to Syndrome of Inappropriate Anti-Diuretic Hormone secretion (SIADH).
- Febrile seizures - 25%
- Haemolytic Uraemic Syndrome (HUS)
- HUS complicates 10% of infections with Shigella dysenteriae. HUS is the most frequent cause of acute renal failure among young children worldwide. It is most often due to infection with enterohaemorrhagic Escherichia coli (particularly type O157:H7), but may also be caused by infection with Shigella dysenteriae 1.
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