What is severe dengue?

Severe Dengue

Severe dengue is defined by the World Health Organization as dengue infection complicated by severe plasma leakage leading to shock or fluid accumulation with respiratory distress, severe bleeding, or organ failure (including liver damage with AST/ALT >1000 IU/L, impaired consciousness, or heart/kidney involvement). 1

Clinical Manifestations of Severe Dengue

The three cardinal features that distinguish severe dengue from uncomplicated disease are:

• Severe plasma leakage manifesting as dengue shock syndrome (systolic BP <90 mmHg for >30 minutes or pulse pressure <20 mmHg despite initial fluid resuscitation) or fluid accumulation causing respiratory distress 2, 1
• Severe bleeding that is clinically significant (not just petechiae or positive tourniquet test), often occurring in combination with profound shock and leading to disseminated intravascular coagulation 3
• Severe organ impairment including hepatic injury (transaminases >1000 IU/L), impaired consciousness/encephalopathy, or cardiac/renal failure 1

Dengue Shock Syndrome: The Most Critical Presentation

Dengue shock syndrome represents the most life-threatening form of severe dengue and requires immediate recognition:

• Narrow pulse pressure <20 mmHg is an earlier and more sensitive indicator than absolute hypotension and should trigger immediate aggressive fluid resuscitation 2
• Signs of end-organ hypoperfusion include cold/clammy extremities, capillary refill time ≥3 seconds, elevated lactate >2 mmol/L, and altered mental status 2
• The case fatality rate can reach 44% without appropriate management, but drops to <0.5% with early recognition and proper fluid therapy 2, 4

Pathophysiology

The underlying mechanism distinguishing severe dengue involves:

• Increased vascular permeability causing massive plasma leakage from the intravascular to extravascular compartment, resulting in hemoconcentration (rising hematocrit) and hypovolemic shock 3, 4
• This plasma leakage, combined with thrombocytopenia, hypoxia, and acidosis, creates the perfect storm for multiple organ failure 3
• Severe dengue typically follows secondary infection with a different dengue serotype, where antibody-dependent enhancement amplifies viral replication 4

Critical Timing

• Warning signs typically appear on days 3-7 of illness, coinciding with defervescence (fever resolution), which paradoxically marks the beginning of the critical phase 2
• This critical phase lasts 24-48 hours and represents the window when patients can rapidly deteriorate from dengue with warning signs to severe dengue 2

Warning Signs That Precede Severe Dengue

Recognizing these warning signs allows intervention before progression to severe disease:

• Persistent vomiting preventing oral intake 2
• Severe abdominal pain or tenderness (particularly right upper quadrant from hepatic involvement) 2
• Clinical fluid accumulation (pleural effusion, ascites) 2
• Mucosal bleeding (epistaxis, gum bleeding, hematemesis) 2
• Lethargy or restlessness 2
• Hepatomegaly >2 cm 2
• Rising hematocrit concurrent with rapid platelet decline (this laboratory pattern indicates ongoing plasma leakage) 2

Distinction from Dengue Hemorrhagic Fever

While the older WHO classification used "dengue hemorrhagic fever" (DHF) as a separate category, the revised system incorporates this into "severe dengue":

• DHF was defined as acute febrile illness with minor/major bleeding, thrombocytopenia ≤100,000/mm³, and evidence of plasma leakage 1
• The revised classification has superior sensitivity (92.1%) and specificity (78.5%) for identifying patients requiring intensive care compared to the older DHF/DSS system 2
• Major bleeding in dengue almost invariably occurs in combination with profound shock, not as an isolated phenomenon 3

Management Implications

• Immediate fluid resuscitation with 20 mL/kg isotonic crystalloid bolus over 5-10 minutes is the cornerstone of severe dengue management, with reassessment after each bolus 5, 2
• For severe shock with pulse pressure <10 mmHg, colloid solutions show benefit for faster resolution compared to crystalloids alone 5
• Pregnant women with dengue have nearly 3-fold higher risk of developing dengue shock syndrome (15% vs 5% in non-pregnant individuals), warranting lower threshold for hospitalization 6

Common Pitfall

The most critical error is failing to recognize that fever resolution does not signal recovery—it marks the beginning of the dangerous critical phase when plasma leakage accelerates and shock can develop within hours. 2