What is the recommended initial test for suspected typhoid fever?

Recommended Initial Test for Typhoid Fever

Blood culture is the gold standard and recommended initial test for suspected typhoid fever, with 2-3 specimens of 20 mL each (in adults) collected prior to antibiotic administration. 1, 2

Primary Diagnostic Approach

Obtain blood cultures immediately when typhoid fever is suspected, as this remains the definitive diagnostic test endorsed by the Infectious Diseases Society of America and American College of Physicians. 1, 2

Key Collection Parameters:

• Volume matters: Collect 20 mL per specimen in adults (2-3 separate specimens) because the bacteremia level in typhoid is extremely low at only 0.3 colony-forming units/mL 1, 2
• Timing is critical: Highest yield occurs in the first week of symptoms, with sensitivity ranging from 40-80% (or approximately 50% compared to bone marrow culture) 1, 2
• Pre-antibiotic collection: Always obtain cultures before starting antimicrobials to maximize sensitivity 2, 3

When Blood Culture Fails or Is Insufficient

Bone marrow culture is more sensitive than blood culture and should be reserved for specific scenarios: 1, 2

• Antibiotics have already been administered
• Blood cultures remain negative despite high clinical suspicion
• Patient has received prior antimicrobial therapy

Adjunctive Testing Options:

• Stool, duodenal fluid, and urine cultures can be beneficial as complementary tests, particularly when blood cultures are negative 1, 2
• Molecular diagnostics (culture-independent methods) can be used from stool and blood when available, though they detect DNA rather than viable organisms and require clinical context for interpretation 1, 2

Tests to AVOID

Do NOT use serologic tests including the Widal test or Typhidot for diagnosis—these have poor sensitivity and specificity and are explicitly not recommended by the CDC and Infectious Diseases Society of America. 2, 3

Special Populations

For infants: Blood culture remains the gold standard, as serological tests are particularly unreliable in this age group; collect multiple samples before starting IV ceftriaxone 3

Critical Pitfalls to Avoid

• Insufficient blood volume: Collecting less than 20 mL per specimen significantly reduces detection rates given the low-level bacteremia 1, 2
• Starting antibiotics first: This dramatically reduces blood culture sensitivity; always culture before treating unless the patient is in septic shock 2, 3
• Relying on serology alone: The CDC explicitly states that isolation of Salmonella typhi from clinical specimens is required for confirmation, not serologic evidence 2

Public Health Requirement

All positive specimens must be cultured in clinical or public health laboratories (even if initially detected by molecular methods) to enable antimicrobial susceptibility testing and outbreak detection. 2