🦠 Typhoid Fever – Tests, Types & Reliability (Reality Check)

1️⃣ Blood Culture – GOLD STANDARD

• Live Salmonella typhi / paratyphi bacteria

🕒 Best time

• 1st week of fever (before antibiotics)

✅ Reliability

• Specificity: ~100%

• Sensitivity:

  • 60–80% (early, before antibiotics)

  • Drops sharply after antibiotics

👍 Advantages

✔ Confirms diagnosis
✔ Gives antibiotic sensitivity
✔ Differentiates typhi vs paratyphi

👎 Limitations

❌ Time-consuming (48–72 hrs)
❌ False negative if antibiotics already taken

📌 Clinical take:
👉 Best test if patient presents early

2️⃣ Widal Test – MOST MISUSED

🔬 What it detects

• Antibodies (O & H) against Salmonella

🕒 Best time

• After 7–10 days of fever

❌ Reliability

• Low

• False positives common in:

  • Endemic areas (India)

  • Past infection

  • Vaccination

  • Other infections (malaria, dengue)

🚩 Problems

❌ Single Widal test is NOT diagnostic
❌ Baseline titres vary by region

✔ When useful

• Paired sera (4-fold rise after 7 days)
  → Rarely done in real life

📌 Clinical take:
👉 Avoid using Widal alone to diagnose typhoid

3️⃣ Typhidot (IgM / IgG)

🔬 What it detects

• IgM & IgG antibodies against S. typhi antigens

🕒 Best time

• From 5–7 days of fever

✅ Reliability

• Sensitivity: 70–90%

• Specificity: 75–85%

👍 Advantages

✔ Faster than culture
✔ Better than Widal
✔ IgM → recent infection

👎 Limitations

❌ Cannot assess antibiotic sensitivity
❌ IgG may persist → false positives

📌 Clinical take:
👉 Useful when culture not available or patient already on antibiotics

4️⃣ Rapid Card Tests (ICT)

🔬 Examples

• TUBEX TF

• Other lateral flow kits

Reliability

• Variable & kit-dependent

📌 Clinical take:
👉 Use only as supportive, not confirmatory

5️⃣ Stool / Urine Culture

🕒 Best time

• 2nd–3rd week

Role

• Detects carrier state

• Limited value in acute diagnosis

🔬 COMPARISON TABLE (Quick OPD Reference)

🧠 PRACTICAL CLINICAL APPROACH (India)

🟢 Fever < 7 days

➡ Blood culture ± Typhidot IgM

🟡 Fever > 7 days

➡ Typhidot IgM + clinical correlation
➡ Avoid relying on single Widal

🔴 Already on antibiotics

➡ Culture sensitivity ↓
➡ Use Typhidot + CBC + LFT + clinical picture

⚠️ COMMON MISTAKES TO AVOID

❌ Treating based on single Widal report
❌ Ignoring dengue, malaria, viral hepatitis
❌ Missing drug-resistant typhoid (culture skipped)

🩺 KEY TAKE-HOME MESSAGE

Blood culture = best test
Typhidot > Widal
Widal alone is unreliable in endemic areas

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