What pathology test is used to diagnose typhoid, paratyphoid, and dysentery?

Diagnostic Tests for Typhoid, Paratyphoid, and Dysentery

Blood culture is the gold standard diagnostic test for typhoid and paratyphoid fever, while stool culture is the primary diagnostic method for dysentery. 1

Diagnostic Tests for Typhoid and Paratyphoid Fever

First-line Testing

• Blood culture: 40-80% sensitivity, highest yield in first week of illness 1
  • Requires 2-3 blood cultures of 20mL each for adults 2
  • Lower volumes may be sufficient for children who have higher magnitudes of bacteremia 2
  • Should be collected before antimicrobial administration to maximize sensitivity 2

Additional Testing for Typhoid/Paratyphoid

• Stool culture: 35-65% sensitivity, positive after first week of illness 1
• Bone marrow culture: Higher sensitivity than blood culture, particularly valuable if antimicrobials have been administered 2, 1
• Duodenal fluid culture: May be beneficial to detect enteric fever 2
• Urine culture: 0-58% sensitivity, positive after first week 1

Tests to Avoid for Typhoid/Paratyphoid

• Serologic tests (including Widal test): Not recommended due to poor sensitivity and specificity 2, 1
• Rapid serological tests (Typhidot, Typhidot-M, Tubex): Show mixed results and should not be relied upon for diagnosis 1, 3

Diagnostic Tests for Dysentery

First-line Testing

• Stool culture: Primary diagnostic method for bacterial causes of dysentery (Shigella, Campylobacter, etc.) 2
• Molecular diagnostic tests: Nucleic acid amplification tests (NAATs) from stool specimens for detection of bacterial, viral, and parasitic causes 2

Additional Testing for Specific Dysentery Pathogens

• Shigella: Routine stool culture or NAAT 2
• Entamoeba histolytica (amebic dysentery): Species-specific immunoassay or NAAT from stool 2
• Campylobacter: Routine stool culture or NAAT 2

Specimen Collection Guidelines

• Optimal specimen: Diarrheal stool sample (takes shape of container) 2
• Alternative: Rectal swab if timely diarrheal stool cannot be collected (for bacterial infections) 2
• Fresh stool: Preferred for viral, protozoal agents, and C. difficile toxin detection 2

Common Pitfalls to Avoid

• Relying solely on serologic tests like the Widal test for typhoid diagnosis 1
• Failing to collect blood cultures before starting antibiotics 1
• Using multiple stool specimens for C. difficile testing (does not increase yield) 2
• Overlooking typhoid fever in patients with fever but without diarrhea 1
• Using fecal leukocyte examination or stool lactoferrin detection to establish cause of infectious diarrhea 2

Testing Algorithm

1. For suspected typhoid/paratyphoid fever:

   • Collect blood cultures (before antibiotics)
   • Follow with stool and urine cultures
   • Consider bone marrow culture if patient has received antibiotics
   • Do not rely on serologic tests

2. For suspected dysentery:

   • Collect stool sample for culture and/or molecular testing
   • Request specific testing for suspected pathogens based on clinical presentation and epidemiology
   • Consider additional specialized testing for parasitic causes if indicated

By following this evidence-based approach to diagnostic testing, clinicians can optimize the detection of typhoid, paratyphoid, and dysentery pathogens, leading to appropriate treatment and improved patient outcomes.