Dengue

The patient's hematocrit is rising while their platelet count is crashing — most diseases don't do both at once. This one does, and it means plasma is leaking out of the blood vessels.

Dengue virus has four serotypes (DENV 1–4), transmitted by the day-biting Aedes aegypti mosquito (peak activity 6 AM–6 PM, urban areas, breeds in small collections of standing water). First infection with any serotype is usually mild or asymptomatic. Second infection with a DIFFERENT serotype carries significantly higher risk for severe dengue due to antibody-dependent enhancement. Presentation: sudden high fever (40°C, 'breakbone fever'), severe retro-orbital headache, myalgia, arthralgia, and a maculopapular rash appearing 3–5 days after fever onset. Laboratory findings include leukopenia and thrombocytopenia. Dengue hemorrhagic fever (DHF) warning signs typically appear around defervescence (day 3–7 as fever breaks): persistent vomiting, severe abdominal pain, mucosal bleeding (gingival, epistaxis, vaginal), restlessness or lethargy, hepatomegaly >2 cm, and the critical laboratory finding — rising hematocrit concurrent with rapidly falling platelet count. This combination indicates plasma leakage from increased vascular permeability. Dengue shock syndrome (DSS): progression to circulatory failure with narrow pulse pressure (<20 mmHg), weak rapid pulse, cold clammy extremities, altered consciousness. Diagnosis: NS1 antigen testing (positive in first 5 days), IgM/IgG serology (positive after day 5). The tourniquet test (inflate BP cuff between systolic and diastolic for 5 minutes; ≥20 petechiae per 1-inch square is positive) serves as a bedside screening tool. Treatment: NO antiviral exists. Management is entirely supportive. Oral rehydration is first-line for mild cases. IV isotonic crystalloids (normal saline or lactated Ringer's) for DHF with signs of plasma leakage — the goal is to maintain adequate circulation during the 24–48 hour critical phase. Acetaminophen for fever and pain — aspirin and NSAIDs are CONTRAINDICATED (increase bleeding risk in thrombocytopenic patients). Platelet transfusion only for active hemorrhage, not for a low count alone. Serial monitoring: hematocrit and platelet count every 4–6 hours during the critical phase. Prevention: eliminate standing water (breeding sites), use insect repellent, window screens, long sleeves during daytime. Dengvaxia vaccine has limited indications. Nursing: implement bleeding precautions (soft toothbrush, electric razor, no IM injections, avoid rectal temperatures), strict I&O with daily weights, monitor for signs of shock (restlessness, tachycardia, narrowing pulse pressure), and educate that the most dangerous phase is when the fever BREAKS, not when it's highest.

Key Distinctions

Rising hematocrit plus falling platelets is the hallmark of plasma leakage — this distinguishes dengue hemorrhagic fever from uncomplicated dengue. The most dangerous period is during defervescence (fever breaking), not during high fever — students expect deterioration with fever and may relax monitoring as temperature drops. Aspirin and NSAIDs are absolutely contraindicated — use acetaminophen only. Do not transfuse platelets based on count alone; transfuse only for active bleeding. Aedes mosquitoes bite during the DAY (unlike malaria's Anopheles which bite at night) — prevention strategies differ.

Clinical Pearl

The fever breaks and everyone relaxes — that's exactly when dengue kills. Defervescence is the danger zone, not the fever.