Definition/General
Introduction:
Infectious colitis is acute or chronic inflammation of the colon caused by bacterial, viral, parasitic, or fungal pathogens
Shows variable clinical presentation from mild diarrhea to fulminant colitis
Histologic patterns vary by organism
Common in developing countries including India.
Origin:
Caused by pathogenic microorganisms invading colonic mucosa
Results from direct tissue invasion or toxin-mediated damage
Shows acute inflammatory response
Associated with poor sanitation and contaminated food/water
Immunocompromised patients at higher risk.
Classification:
Bacterial colitis: Salmonella, Shigella, Campylobacter, E
coli, C
difficile
Viral colitis: CMV, HSV, adenovirus
Parasitic colitis: Entamoeba histolytica, Giardia, Cryptosporidium
Fungal colitis: Candida, mucormycosis
Mycobacterial colitis: tuberculosis.
Epidemiology:
High incidence in developing countries
All age groups affected
Seasonal variation (summer months)
Travel-associated infections common
Immunocompromised patients at risk
Foodborne outbreaks frequent.
Clinical Features
Presentation:
Acute diarrhea (most common)
Abdominal pain and cramping
Fever (60-80% cases)
Nausea and vomiting
Bloody stools (invasive organisms)
Dehydration.
Symptoms:
Watery or bloody diarrhea
Tenesmus (invasive colitis)
Lower abdominal cramping
Urgency
Constitutional symptoms (fever, malaise)
Mucus passage.
Risk Factors:
Travel to endemic areas
Contaminated food/water
Poor sanitation
Immunocompromised state
Antibiotic use (C
difficile)
Hospitalization
Daycare attendance.
Screening:
Stool culture (bacterial pathogens)
Stool microscopy (parasites)
Antigen detection tests
PCR panels (multiple pathogens)
Colonoscopy (severe cases)
Tissue biopsy (diagnosis).
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Gross Description
Appearance:
Mucosal erythema and edema
Ulceration (invasive organisms)
Pseudomembrane formation (C
difficile)
Hemorrhage and congestion
Friable mucosa
Variable distribution.
Characteristics:
Hyperemic mucosa
Shallow ulcerations
Mucosal sloughing
Purulent exudate
Edematous bowel wall
Loss of normal fold pattern.
Size Location:
Variable distribution by organism
Left-sided colitis (Shigella)
Right-sided involvement (Salmonella, Yersinia)
Pancolitis (severe infections)
Terminal ileum (Yersinia, Salmonella).
Multifocality:
Diffuse involvement (most cases)
Patchy distribution (some organisms)
Skip lesions possible
Rectal involvement variable
Small bowel involvement (some pathogens).
Microscopic Description
Histological Features:
Acute inflammatory infiltrate
Neutrophilic invasion of crypts
Crypt abscesses
Surface epithelial necrosis
Mucosal ulceration
Edema and congestion.
Cellular Characteristics:
Neutrophils (predominant acute inflammation)
Lymphocytes and plasma cells
Eosinophils (parasitic infections)
Viral inclusions (CMV, HSV)
Organisms (bacteria, parasites).
Architectural Patterns:
Preserved crypt architecture (acute cases)
Crypt distortion (chronic cases)
Surface ulceration
Cryptitis and crypt abscesses
Pseudomembrane formation (specific organisms).
Grading Criteria:
Mild: minimal inflammation, preserved architecture
Moderate: cryptitis, crypt abscesses, surface erosion
Severe: extensive ulceration, transmural inflammation
Organism-specific patterns.
Immunohistochemistry
Positive Markers:
CMV (CMV colitis - nuclear and cytoplasmic)
HSV (HSV colitis)
Adenovirus (adenoviral colitis)
CD68 (macrophages)
Myeloperoxidase (neutrophils).
Negative Markers:
Non-specific bacterial antigens (unless specific stains)
Malignancy markers
IBD-associated markers
Autoimmune markers.
Diagnostic Utility:
Viral antigen detection (CMV, HSV, adenovirus)
Confirms viral etiology
Excludes other causes
Tissue-based diagnosis when cultures negative
Immunocompromised patients.
Molecular Subtypes:
Bacterial subtypes (invasive vs toxigenic)
Viral subtypes (CMV, HSV, adenovirus)
Parasitic subtypes (protozoa, helminths)
Mixed infections possible.
Molecular/Genetic
Genetic Mutations:
Pathogen-specific genes
Virulence factors
Antibiotic resistance genes
Host susceptibility genes
Immune response genes.
Molecular Markers:
Pathogen-specific antigens
Inflammatory cytokines (IL-1β, TNF-α, IL-8)
Bacterial toxins
Viral proteins
Parasitic antigens.
Prognostic Significance:
Organism type (virulence)
Host immune status
Extent of involvement
Early treatment
Complications (perforation, bleeding).
Therapeutic Targets:
Antibiotics (bacterial infections)
Antivirals (CMV, HSV)
Antiparasitic agents
Supportive care
Probiotics (adjunctive).
Differential Diagnosis
Similar Entities:
Inflammatory bowel disease
Ischemic colitis
Drug-induced colitis
Radiation colitis
Pseudomembranous colitis
Neutropenic colitis.
Distinguishing Features:
Infectious colitis: Organisms identified, acute onset, travel history
IBD: Chronic changes, architectural distortion
Ischemic: Watershed zones, older age
Drug-induced: Medication history
C
difficile: Antibiotic history, pseudomembranes.
Diagnostic Challenges:
Identifying specific organisms
Distinguishing from IBD (clinical correlation)
Recognizing viral inclusions
Detecting parasites
Mixed infections.
Rare Variants:
Necrotizing enterocolitis
Neutropenic enterocolitis
Hemorrhagic colitis
Chronic infectious colitis
Opportunistic infections.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[specimen type] from [anatomical location]
Clinical Information
Acute diarrhea. Travel history: [yes/no]. Immunocompromised: [yes/no]
Inflammatory Pattern
Acute inflammation: [mild/moderate/severe]. Cryptitis and crypt abscesses: [present/absent]
Organism Identification
Organisms identified: [bacteria/parasites/viral inclusions/none seen]. Special stains: [performed/recommended]
Special Features
Viral inclusions: [present/absent]. Pseudomembranes: [present/absent]. Eosinophilia: [present/absent]
Complications
Ulceration: [present/absent]. Perforation: [present/absent]. Hemorrhage: [present/absent]
Recommendations
Stool culture and microscopy recommended. PCR panel may be helpful. Clinical correlation advised.
Final Diagnosis
Acute [infectious/bacterial/viral/parasitic] colitis - [specific organism if identified]