Shigella Infection
Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management
Definition
Shigella infection (shigellosis) is a highly contagious bacterial infection of the gastrointestinal tract, causing dysentery characterised by diarrhoea, fever, and abdominal cramps.
Aetiology
- Caused by Shigella species: S. dysenteriae, S. flexneri, S. sonnei, S. boydii.
- Transmission via faecal oral route through contaminated food, water, or direct person to person contact.
- Low infectious dose (<100 bacteria) makes transmission highly efficient.
Pathophysiology
- Shigella invades colonic epithelial cells, leading to inflammatory destruction of the mucosa.
- Production of Shiga toxin (in some strains) contributes to severe colitis and haemolytic uraemic syndrome (HUS).
- Inflammation and ulceration cause bloody diarrhoea, fever, and abdominal cramping.
Risk Factors
- Poor sanitation and overcrowded living conditions.
- Young children (day care centres, schools).
- Immunocompromised individuals (HIV, chemotherapy patients).
- International travel to endemic regions.
- Sexual contact involving faecal oral transmission.
Signs and Symptoms
- Sudden onset of watery diarrhoea, progressing to bloody and mucoid stools.
- Severe abdominal cramps and tenesmus.
- Fever, malaise, and anorexia.
- Dehydration in severe cases.
- Complications: haemolytic uraemic syndrome (HUS), reactive arthritis, toxic megacolon.
Investigations
- Stool culture: confirms Shigella species and guides antibiotic therapy.
- Stool microscopy: presence of leukocytes and red blood cells.
- Shiga toxin assay: if S. dysenteriae is suspected.
- Full blood count (FBC): may show leukocytosis.
- Renal function tests: assess for complications such as HUS.
Management
1. Supportive Care:
- Oral rehydration therapy (ORT) for mild dehydration.
- IV fluids for severe dehydration.
- Avoid antimotility agents (e.g., loperamide) due to risk of toxic megacolon.
2. Antibiotic Therapy (For Severe Cases):
- First line: ciprofloxacin or azithromycin.
- Alternatives: ceftriaxone or trimethoprim-sulfamethoxazole.
3. Prevention:
- Good hand hygiene and proper food handling.
- Improvement of sanitation and access to clean water.
- Public health measures to prevent outbreaks in high-risk settings.
4. Referral:
- Infectious diseases: for antibiotic resistant or recurrent cases.
- Nephrology: if haemolytic uraemic syndrome develops.
- Public health: for outbreak investigation and reporting.