Role of Stool Exams in Diagnosing Typhoid Fever
Stool cultures may be beneficial as adjunct diagnostic tests for typhoid fever, but they should not replace blood culture as the primary diagnostic method. 1, 2
Primary Diagnostic Approach
Blood culture remains the gold standard for diagnosing typhoid fever, with sensitivity of 40-80% (highest in the first week of symptoms), and should be performed in all patients with suspected enteric fever. 2
Draw 2-3 blood culture specimens of 20 mL each in adults prior to antibiotic administration, as the bacteremia level is extremely low (0.3 CFU/mL), requiring larger volumes to maximize detection. 1, 2
Bone marrow culture is more sensitive than blood culture (particularly valuable if antimicrobial agents have already been administered), though it is more invasive and technically complex. 1, 2
When to Use Stool Cultures
Stool cultures, along with duodenal fluid and urine cultures, may be beneficial as adjuncts to blood culture for detecting enteric fever, though the recommendation strength is weak. 1, 2
Culture-independent molecular diagnostics from stool specimens (including panel-based multiplex molecular diagnostics) should be performed when there is clinical suspicion of enteric fever. 1
Culturing 2 grams rather than 1 gram of stool increases the isolation rate by 10.5%, with selenite F and selenite mannitol performing equally well as enrichment media. 3
Important Caveats
Stool cultures have lower sensitivity than blood cultures in the acute phase of typhoid fever, as bacteremia precedes stool shedding in the disease course. 3, 4
A positive stool culture can indicate either active infection or chronic carrier state, making interpretation more complex than blood culture results. 3
Stool cultures are more useful for epidemiological typing and outbreak investigations than for acute diagnosis, as they can provide isolates for antibiotic susceptibility testing and molecular characterization. 1
What NOT to Use
Serologic tests (including Widal test) should NOT be used to diagnose enteric fever due to poor performance characteristics, despite their widespread use in some settings. 1, 2, 5
Nucleic acid amplification tests lack sensitivity for detection of Salmonella Typhi in blood, though RT-LAMP methods show promise in research settings with improved sensitivity over conventional culture. 1, 6
Clinical Context
Only 51.5% of clinically diagnosed typhoid cases are bacteriologically confirmed, emphasizing the critical importance of laboratory confirmation rather than relying on clinical diagnosis alone. 4
Stool cultures become more relevant for identifying chronic carriers (those shedding bacteria beyond 12 months after acute infection) rather than for acute diagnosis. 3