A 32-year-old woman from Mumbai presents on day 5 of fever with complaints of severe retro-orbital pain, myalgia, and a blanching maculopapular rash over the trunk and extremities. Temperature is 38.5°C, blood pressure 100/64 mmHg, heart rate 92/min. Laboratory findings show platelet count 85,000/μL, haemoglobin 14 g/dL, haematocrit 42%, and normal liver function tests. Dengue NS1 antigen is positive. Which of the following best describes the current phase of dengue infection?

Explanation

## Clinical Phase Identification This patient is in the **febrile phase with early defervescence** (day 5 of illness). ### Dengue Infection Timeline | Phase | Duration | Key Features | Laboratory Findings | |-------|----------|--------------|---------------------| | **Febrile** | Days 1–7 | Fever, myalgia, retro-orbital pain, rash | NS1 antigen positive, mild thrombocytopenia, normal haematocrit | | **Critical** | Days 3–7 (defervescence) | Plasma leakage, shock risk, bleeding | Platelet nadir, rising haematocrit, pleural effusion | | **Recovery** | Days 7–10+ | Defervescence, improvement | Platelet recovery, normalizing haematocrit | ### Why This Is Febrile Phase **Key Point:** Day 5 of fever with positive NS1 antigen confirms active viral replication phase. The blanching maculopapular rash is classic for dengue fever. **Clinical Pearl:** Platelet count of 85,000/μL is mild thrombocytopenia typical of early febrile phase. The **haematocrit is normal (42%)**, which rules out plasma leakage (critical phase would show rising haematocrit ≥20% increase from baseline). **High-Yield:** The critical phase begins at **defervescence** (when fever breaks), not during fever. This patient still has fever (38.5°C), so she has not yet entered the critical phase. ### Dengue Phases Mnemonic **"FeCRY"** — **Fe**brile → **C**ritical → **R**ecovery → **Y**ou're done - **Febrile**: Fever + rash + myalgia + NS1+ | Mild thrombocytopenia | Normal Hct - **Critical**: Defervescence + plasma leakage risk | Platelet nadir | Rising Hct, pleural effusion - **Recovery**: Platelet recovery | Normalization of labs