Dengue Warning Signs

WHO 2009 Classification (3 Tiers)

The WHO 2009 classification divides dengue into three severity tiers:

Tier	Definition
Dengue without warning signs	Fever + ≥2 of: nausea/vomiting, rash, aches and pains, leukopenia, positive tourniquet test
Dengue with warning signs	Above criteria + any warning sign (see below)
Severe dengue	Any of: severe plasma leakage/shock, severe bleeding, severe organ dysfunction

The 7 Warning Signs (WHO)

These appear in the late febrile phase (days 3-7), typically around the time of or just after defervescence:

Abdominal pain or tenderness - severe, persistent epigastric or right upper quadrant pain
Persistent vomiting - prevents adequate oral intake or rehydration
Clinical fluid accumulation - ascites, pleural effusion (especially right-sided), pericardial effusion detected clinically or on imaging
Mucosal bleeding - gum bleeding, epistaxis, vaginal bleeding, blood in urine/stool
Lethargy or restlessness - altered mental status, may indicate reduced brain perfusion
Liver enlargement >2 cm - hepatomegaly beyond 2 cm below the costal margin
Rising hematocrit with rapid decline in platelet count - hemoconcentration (hematocrit rise ≥20% from baseline) concurrent with rapidly falling platelets

Patients with warning signs will probably recover with early IV rehydration, but without prompt action some progress to severe dengue. - Park's Textbook of Preventive and Social Medicine

The Three Phases of Dengue Illness

Course of dengue illness showing febrile, critical, and recovery phases with temperature, laboratory changes, and potential clinical complications

Phase 1: Febrile (Days 1-3)

Sudden high fever (up to 40-41°C), facial flushing, severe headache
Retro-orbital pain, myalgia/arthralgia ("breakbone fever")
Anorexia, vomiting, epigastric discomfort
Positive tourniquet test (≥10 petechiae per 2.5x2.5 cm square), maculopapular rash

Phase 2: Critical (Days 3-7) - when warning signs emerge

Fever defervesces to ≤37.5-38°C
Plasma leakage begins due to increased capillary permeability
Hematocrit rises as intravascular fluid leaks out
Platelet count drops rapidly (thrombocytopenia, often <100,000 cells/mm³)
Pleural effusions and ascites may develop
Shock and hemorrhage can occur if plasma leakage is severe
Critical plasma leakage phase lasts only 24-48 hours

Phase 3: Recovery

Gradual reabsorption of extravasated fluid
Risk of fluid overload (especially if IV fluids were overcorrected)
Platelet count recovers, hematocrit may fall (from hemodilution as fluid re-enters circulation)

Criteria for Severe Dengue

Severe dengue is diagnosed when any of the following are present:

Severe plasma leakage leading to dengue shock syndrome (DSS) or fluid accumulation with respiratory distress
Severe bleeding as assessed by a clinician
Severe organ dysfunction: AST or ALT ≥1,000 IU/L, impaired consciousness, cardiac failure, or other organ failure

Dengue Shock Syndrome (DSS) - Signs to Recognize

Tachycardia, cool extremities, delayed capillary refill, weak/thready pulse
Lethargy or restlessness (reduced brain perfusion)
Pulse pressure ≤20 mmHg with raised diastolic pressure (e.g., 100/80 mmHg)
Frank hypotension (late and ominous sign)

Special Populations at Higher Risk of Severe Disease

Infants of dengue-immune mothers
Children >1 year old
Patients with second or subsequent dengue infection (heterotypic reinfection - immune enhancement)
Females more commonly affected than males
After age 12, susceptibility to severe dengue drops considerably

Tourniquet Test (Capillary Fragility Test)

Inflate BP cuff to midpoint between systolic and diastolic pressure for 5 minutes. A positive result is ≥10 petechiae per 2.5x2.5 cm area. In DHF, typically ≥20 petechiae are seen.

Sources:

Red Book 2021 (AAP Committee on Infectious Diseases), p. 520-521
Park's Textbook of Preventive and Social Medicine, p. 292-293
Harrison's Principles of Internal Medicine, 22nd Ed. (2025)
Tintinalli's Emergency Medicine: A Comprehensive Study

This is a shared conversation. Sign in to Orris to start your own chat.