Shigellosis (Bacillary Dysentery)

Shigellosis is an acute intestinal infection caused by Shigella species, which are gram-negative, facultatively anaerobic bacteria. It is a major cause of bacillary dysentery worldwide, particularly in areas with poor sanitation and overcrowding. Shigellosis can present as a self-limited disease or a severe, life-threatening condition, especially in children, the elderly, or immunocompromised individuals.

Etiology and Pathophysiology:

• Shigella species are divided into four major groups:
  1. Group A: Shigella dysenteriae (most severe, can produce Shiga toxin)
  2. Group B: Shigella flexneri (common in developing countries)
  3. Group C: Shigella boydii (less common)
  4. Group D: Shigella sonnei (predominant in industrialized nations)

The pathogenesis of shigellosis involves:

1. Ingestion of the organism: Shigella bacteria are transmitted via the fecal-oral route, commonly through contaminated food, water, or direct person-to-person contact.
2. Colonization of the colon: The bacteria attach to and invade the colonic mucosa, primarily in the distal ileum and colon. They penetrate the intestinal epithelial cells through M cells located in Peyer’s patches.
3. Intracellular multiplication and spread: After invading the epithelial cells, Shigella bacteria multiply within the cytoplasm and spread to adjacent cells, causing cell death, tissue damage, and an intense inflammatory response.
4. Shiga toxin production (in S. dysenteriae type 1): This exotoxin inhibits protein synthesis in host cells, leading to further epithelial damage and complications like hemolytic-uremic syndrome (HUS).

Epidemiology:

• Shigellosis is prevalent worldwide, with higher incidence in tropical and subtropical regions where sanitation is poor.
• High-risk populations include:
  • Children under five years of age
  • Elderly individuals
  • Immunocompromised patients (e.g., HIV/AIDS)
  • Institutionalized populations (e.g., prisons, daycares)
  • Travelers to endemic regions

Clinical Manifestations:

The clinical presentation varies depending on the Shigella species and host factors but typically includes:

1. Incubation period: Ranges from 1 to 7 days, usually 2-3 days.
2. Initial symptoms: Include fever, malaise, and abdominal cramps. This may be followed by watery diarrhea.
3. Dysenteric phase: Characterized by frequent, small-volume, bloody, and mucoid stools accompanied by severe abdominal cramps and tenesmus (painful straining during defecation). The dysentery is a result of mucosal invasion and inflammation in the colon.
4. Complications:
   • Severe dehydration: Due to fluid loss, especially in young children and the elderly.
   • Sepsis: More common in malnourished individuals or those with compromised immune systems.
   • Hemolytic-uremic syndrome (HUS): Particularly associated with S. dysenteriae type 1 and characterized by acute kidney injury, hemolytic anemia, and thrombocytopenia.
   • Toxic megacolon: Rare but serious, involving severe colonic distention.
   • Neurological complications: Such as seizures, which are more common in children.

Diagnosis:

1. Stool culture:
   • The gold standard for diagnosing shigellosis, with isolation of Shigella species confirming the infection.
   • Sensitivity testing should be performed to guide antibiotic therapy due to increasing antibiotic resistance.
2. Stool microscopy:
   • May show leukocytes and red blood cells, suggesting an invasive bacterial pathogen.
3. PCR testing and molecular assays:
   • Detects Shigella DNA and can be useful in settings where culture facilities are limited.
4. Serologic tests:
   • Generally not used in routine diagnosis but may have epidemiological value.

Management:

1. Rehydration therapy:
   • The cornerstone of treatment, particularly for patients with moderate to severe dehydration.
   • Oral rehydration salts (ORS) are preferred for mild to moderate dehydration.
   • Intravenous fluids are indicated in severe dehydration or when oral rehydration is not feasible.
2. Antibiotic therapy:
   • Shortens the duration of illness, reduces transmission, and prevents complications.
   • Empiric therapy should consider local resistance patterns:
     • Ciprofloxacin (500 mg orally twice daily for 3 days): Widely used in adults but increasingly encountering resistance.
     • Azithromycin (500 mg orally once daily for 3 days): An alternative, especially in children.
     • Ceftriaxone (2 g intravenously once daily for 5 days): For severe cases or when oral therapy is not possible.
     • Alternative antibiotics: Such as pivmecillinam or fosfomycin, may be used based on susceptibility.
   • Avoiding antimotility agents: Such as loperamide, as they may worsen the disease by slowing fecal clearance of the pathogen.
3. Management of complications:
   • Severe dehydration: Requires prompt fluid resuscitation with isotonic fluids (e.g., normal saline or Ringer’s lactate).
   • Hemolytic-uremic syndrome (HUS): Managed with supportive care, including dialysis and blood transfusions as needed.
   • Toxic megacolon: Requires prompt medical and potentially surgical management.

Complications:

• Malnutrition and growth retardation: Particularly in children with repeated or chronic infections.
• Post-infectious sequelae: Including reactive arthritis, which may develop weeks after the infection, especially in individuals carrying the HLA-B27 allele.
• Chronic diarrhea: May occur in patients with malnutrition or underlying gastrointestinal diseases.

Prevention and Control:

1. Improving sanitation and hygiene:
   • Handwashing with soap and water is crucial, especially in endemic areas and institutions.
   • Safe disposal of human waste and provision of clean drinking water.
2. Food safety:
   • Proper cooking of food, avoiding raw or contaminated foods, especially in areas with known outbreaks.
3. Vaccination:
   • There is no widely available vaccine for shigellosis, but several candidates are under investigation, including oral and injectable vaccines targeting various Shigella serotypes.
4. Public health measures:
   • Outbreak surveillance and timely interventions in cases of outbreaks, particularly in healthcare settings, schools, and refugee camps.

Advanced Considerations

• Antimicrobial resistance: Shigella species are increasingly resistant to common antibiotics (e.g., ciprofloxacin, trimethoprim-sulfamethoxazole, ampicillin), complicating treatment choices. Understanding local resistance patterns is essential for empirical therapy.
• Treatment in special populations:
  • In pregnant women, azithromycin is generally preferred due to its safety profile.
  • HIV-infected patients may require more aggressive treatment and monitoring for complications.
• Novel therapeutic approaches: The use of probiotics, bacteriophage therapy, and anti-inflammatory agents is under investigation for improving treatment outcomes.

Prognosis:

• Mild cases: Typically resolve within a week with supportive care and antibiotics.
• Severe cases: Have a higher risk of complications, especially in malnourished children, the elderly, and those with comorbidities.
• Recurrent or chronic shigellosis: Can occur in immunocompromised individuals, requiring long-term management strategies.