Diagnosis of Typhoid Fever
Blood culture is the primary diagnostic test for typhoid fever and should be obtained as early as possible, ideally within the first week of symptoms when sensitivity is highest (40-80%). 1
Clinical Suspicion and When to Test
Suspect typhoid fever (enteric fever) in any febrile patient who:
- Has traveled to endemic areas (South/Southeast Asia, sub-Saharan Africa, Central/South America) within the past 30 days 2
- Has consumed food prepared by someone with recent endemic exposure 2
- Has laboratory exposure to Salmonella Typhi 2
- Presents with fever that may or may not be accompanied by diarrhea (diarrhea is actually uncommon in typhoid) 2
Key clinical features include fever (almost invariable), headache, constipation or diarrhea, dry cough, and potentially misleading symptoms like meningism 1. Hepatosplenomegaly and stupor may develop later 2. Laboratory findings are non-specific—blood counts and liver function tests may show almost any pattern of abnormality 1.
Diagnostic Testing Algorithm
First-Line: Culture-Based Diagnosis
Blood cultures (2-3 sets, 20 mL each in adults)
Stool and urine cultures
Bone marrow culture (if available and clinically appropriate)
Culture-Independent Diagnostic Tests (CIDT)
Panel-based multiplex molecular diagnostics from stool and blood can be used when there is clinical suspicion of enteric fever 2. However, these have important limitations:
- Do not provide antimicrobial susceptibility data 2
- Impede public health outbreak detection if isolates are not preserved 2
- Specimens positive by CIDT should still be cultured for susceptibility testing and public health surveillance 2
Tests to AVOID
The Widal test should NOT be used 1—it lacks both sensitivity and specificity and is not recommended despite its historical popularity.
Newer rapid serological tests (Typhidot, Typhidot-M, Tubex) detecting IgM against specific antigens have shown mixed results 1 and are not yet recommended as primary diagnostic tools in guidelines, though research suggests some promise 3.
Serologic tests in general should not be used to diagnose enteric fever 2.
Important Diagnostic Pitfalls
Antibiotic susceptibility testing caveat: Ciprofloxacin disc testing is unreliable for determining fluoroquinolone sensitivity in S. Typhi and S. Paratyphi. The organism must also be sensitive to nalidixic acid on disc testing to be considered truly fluoroquinolone-sensitive 1. This is critical given that >70% of isolates imported to the UK are fluoroquinolone-resistant 1.
Serial testing increases yield: For urine antigen detection and culture, examining serially collected specimens significantly improves sensitivity (from 65% to 95% for blood culture-positive cases) 4.
Vaccination history: Prior typhoid vaccination provides incomplete protection and does not protect against paratyphoid 1. A history of vaccination does not rule out disease.
Timing matters: Blood culture sensitivity is highest early (first week), while stool/urine cultures become positive later (after first week) 1.
Additional Diagnostic Considerations
When enteric fever is suspected, also culture duodenal fluid when indicated 2. In unstable patients with strong clinical suspicion, empirical treatment should be started pending culture results 1, but diagnostic specimens must be obtained first whenever possible.
The diagnosis requires a high index of suspicion based on travel history and clinical presentation, followed by appropriate culture-based testing with attention to timing and specimen selection.