Dengue Fever in Children

Dengue is the commonest arboviral infection in India and a leading cause of febrile illness with thrombocytopenia in children. The paediatric exam favourite is the WHO 2009 classification, the timing of NS1/IgM/IgG serology, and above all the haematocrit-guided fluid management of dengue shock syndrome — where children differ critically from adults.

Etiology & basic virology

• Caused by dengue virus (DENV) — a single-stranded RNA Flavivirus (family Flaviviridae), four serotypes DENV-1, 2, 3, 4.
• Vector: Aedes aegypti (also Aedes albopictus) — a day-biting mosquito, breeds in clean stagnant water, has black-and-white striped legs ("tiger mosquito").
• Infection with one serotype gives lifelong immunity to that serotype only, but transient (months) cross-protection against others. Subsequent infection with a different serotype carries the highest risk of severe disease.
• Incubation period: 4–7 days (range 3–14).

High-yield: Severe dengue is classically linked to secondary infection with a heterologous serotype via Antibody-Dependent Enhancement (ADE) — non-neutralising antibodies from the first infection bind the new serotype and facilitate its entry into Fc-receptor-bearing monocytes, amplifying viral load.

Pathophysiology — the two hallmarks

The whole of severe dengue rests on two phenomena:

1. Plasma leakage — transient increase in capillary permeability (cytokine/complement mediated, especially via NS1 protein and TNF-α, IL-6). Plasma leaks into the pleural and peritoneal spaces → haemoconcentration (rising haematocrit), hypoproteinaemia, effusions, ascites, and ultimately hypovolaemic dengue shock.
2. Haemorrhagic tendency — multifactorial: thrombocytopenia (marrow suppression + immune destruction), platelet dysfunction, vasculopathy, DIC, and consumption.

High-yield: Plasma leakage is selective for these days — it begins around defervescence and lasts 24–48 hours. This window is the critical phase.

The three phases of dengue (the clinical backbone)

Memorise this — most management questions hang on which phase the child is in.

Phase	Timing (from onset)	What is happening	Key danger
Febrile	Day 1–3	High fever, viraemia	Dehydration, febrile seizures (infants), high NS1 yield
Critical	Day 4–6 (around defervescence)	Plasma leakage, HCT rises, platelets fall	Shock, bleeding, organ impairment
Recovery / Convalescent	Day 7 onward	Reabsorption of leaked fluid	Fluid overload, pulmonary oedema, Isle of white in a sea of red rash

High-yield: Shock occurs at defervescence (when the fever falls), NOT at the height of fever. A child who "looks worse as the fever settles" is the classic critical-phase trap.

WHO 2009 classification (replaces old DF / DHF / DSS)

This is the single most tested table. The old DHF/DSS grading (1997) is still asked, but WHO 2009 is the current standard.

Category	Criteria
Dengue without warning signs	Fever + ≥2 of: nausea/vomiting, rash, aches/pains, leucopenia, positive tourniquet test; lives in/travel to endemic area
Dengue WITH warning signs	Above + any warning sign (see below) → admit
Severe dengue	(1) Severe plasma leakage → shock or respiratory distress from effusion; OR (2) severe bleeding; OR (3) severe organ involvement (AST/ALT ≥1000, impaired consciousness, myocarditis)

Warning signs (must memorise — they mandate admission)

Mnemonic "ABCD-L-M":

• Abdominal pain or tenderness
• Bleeding (mucosal)
• Clinical fluid accumulation (ascites, pleural effusion)
• Drowsiness / lethargy / restlessness (altered sensorium)
• Liver enlargement > 2 cm
• Mounting haematocrit with rapid fall in platelets
• (plus persistent vomiting)

High-yield: The combination of a rising haematocrit + rapidly falling platelet count is itself a warning sign — it heralds the onset of plasma leakage even before the child looks sick.

Old WHO 1997 grading of DHF (still examined)

• Grade I: Fever + non-specific symptoms; the only haemorrhagic manifestation is a positive tourniquet test.
• Grade II: Grade I + spontaneous bleeding (skin/other).
• Grade III: Circulatory failure — weak rapid pulse, narrow pulse pressure ≤ 20 mmHg, hypotension, cold clammy skin (= DSS).
• Grade IV: Profound shock — undetectable BP and pulse (= DSS).

High-yield: All four DHF grades require thrombocytopenia (< 100,000/mm³) AND evidence of plasma leakage (HCT rise ≥ 20%, effusion, or hypoproteinaemia). Grade III and IV together = Dengue Shock Syndrome.

Clinical features in children

• Febrile phase: abrupt high-grade fever, retro-orbital pain, headache, myalgia/arthralgia ("break-bone fever"), facial flushing, anorexia, vomiting. Infants and young children may simply have undifferentiated fever ± a rash.
• Rash: early transient macular flush, then on day 5–6 a confluent maculopapular rash with islands of normal skin — "white islands in a sea of red."
• Haemorrhagic: petechiae, positive tourniquet test, epistaxis, gum bleeding, GI bleed, menorrhagia in adolescents.
• Hepatomegaly is common and tender; splenomegaly is rare in young children (more in infants).
• Shock (DSS): restlessness, cold clammy extremities, narrow pulse pressure (≤ 20 mmHg), tachycardia with normal/low BP, prolonged capillary refill (> 2 s), oliguria.

High-yield: Children compensate well and maintain a normal systolic BP even in significant shock (compensated shock) — they crash suddenly. Narrow pulse pressure and tachycardia precede hypotension. This is the key paediatric difference from adults.

Tourniquet (Hess) test

1. Inflate BP cuff to the midpoint between systolic and diastolic pressure.
2. Hold for 5 minutes, deflate, wait 2 minutes.
3. Count petechiae in a 2.5 cm × 2.5 cm (1 inch²) square below the cuff.
4. ≥ 10–20 petechiae per square inch = positive (WHO uses ≥ 10/inch² as positive; ≥ 20 strongly positive).

It indicates capillary fragility; positive in dengue but non-specific (also positive in other thrombocytopenias, scurvy).

Diagnosis & investigation of choice

Diagnostic test choice depends entirely on the day of illness:

Day of illness	Best test	Why
Day 1–5 (febrile/viraemic)	NS1 antigen (ELISA/rapid); RT-PCR	Viraemia present; NS1 detectable from day 1
Day 5 onward	IgM ELISA (MAC-ELISA)	Appears day 4–5, peaks ~2 weeks
Later / past infection	IgG	Rises in primary by day 14; in secondary infection IgG rises early and high

Flow of serology → NS1 (day 1–5) → IgM (after day 5) → IgG (distinguishes primary vs secondary).

High-yield: NS1 antigen is the investigation of choice in the first 5 days; IgM (MAC-ELISA) is the test of choice after day 5. Combining NS1 + IgM gives the best overall sensitivity.

High-yield: In primary infection — IgM high, IgG low/late. In secondary infection — IgG appears early and is high, IgM lower; IgM:IgG ratio < 1.2 (or 1.8 with capture ELISA) suggests secondary dengue.

Supportive labs & monitoring

• CBC: leucopenia (early, useful clue), thrombocytopenia (< 100,000), and the all-important haematocrit.
• Haematocrit (PCV) is the single most important monitoring tool — a ≥ 20% rise from baseline (or from population baseline) = significant plasma leakage; a ≥ 20% fall after fluids = reabsorption/haemodilution or occult bleed.
• USG / chest X-ray: right-sided pleural effusion, ascites, thickened gallbladder wall (sonographic marker of leakage).
• LFTs (AST > ALT, AST ≥ 1000 = severe), serum albumin (low), coagulation profile if bleeding.

Management — the heart of the exam

There is no specific antiviral; management is supportive and fluid-based, dictated by the WHO category.

Group A — dengue without warning signs (outpatient)

• Oral fluids, paracetamol for fever.
• AVOID: aspirin, NSAIDs (ibuprofen, diclofenac), and IM injections — bleeding/Reye risk.
• Daily review; teach warning signs; advise return for any warning sign or at defervescence.

Group B — dengue with warning signs / co-morbidity (admit)

• Isotonic crystalloid (0.9% saline or Ringer lactate) 5–7 mL/kg/hr × 1–2 hr → 3–5 mL/kg/hr × 2–4 hr → 2–3 mL/kg/hr, titrated to HCT and urine output (aim urine ~0.5 mL/kg/hr).
• Reassess HCT and vitals every few hours.

Group C — severe dengue / DSS (the resuscitation question)

Compensated shock (narrow pulse pressure, still has BP):

Isotonic crystalloid bolus 5–10 mL/kg over 1 hour → reassess. If improving, taper (10 → 7 → 5 → 3 mL/kg/hr). If not improving and HCT still high → repeat crystalloid bolus or switch to colloid 10–20 mL/kg.

Hypotensive shock (undetectable/low BP — DSS grade IV):

Crystalloid or colloid bolus 10–20 mL/kg over 10–15 min → reassess HCT.

• If HCT falls but child still in shock → occult haemorrhage → transfuse blood.
• If HCT still high → repeat colloid bolus.

Scenario after fluid bolus	Interpretation	Action
Improving, HCT falling	Recovery	Taper fluids
Still shocked, HCT high	Ongoing leak	Repeat bolus / colloid
Still shocked, HCT now falling	Concealed bleeding	Whole blood / PRBC transfusion

High-yield: In a child still in shock whose haematocrit suddenly drops, the answer is blood transfusion (concealed haemorrhage), NOT more crystalloid.

Platelet transfusion thresholds (exam favourite)

Dengue thrombocytopenia is usually transient and self-resolving — prophylactic platelets are NOT routinely indicated.

Indication	Threshold
Active significant bleeding	Transfuse platelets (any clinically significant bleed)
No bleeding	Transfuse if platelets < 10,000/mm³ (risk of spontaneous bleed)
Pre-procedure / surgery	Maintain > 50,000/mm³

High-yield: Do not transfuse platelets merely for a low count. The triggers are active bleeding or a count < 10,000/mm³. Prophylactic transfusion does not prevent bleeding and may worsen outcomes.

Phase-specific cautions

• During the convalescent phase, leaked fluid is reabsorbed — STOP IV fluids to avoid pulmonary oedema / fluid overload (signs: rising BP with wide pulse pressure, falling HCT, respiratory distress, recovery rash). Furosemide may be needed.
• Total IV fluid duration in the critical phase rarely exceeds 24–48 hours.

Complications

• Dengue shock syndrome and prolonged/refractory shock → multi-organ failure.
• Severe haemorrhage / DIC.
• Fluid overload / pulmonary oedema (often iatrogenic, in convalescence).
• Dengue hepatitis / fulminant hepatic failure (AST > ALT, AST ≥ 1000).
• Expanded dengue syndrome — unusual manifestations: myocarditis, encephalopathy/encephalitis, acute kidney injury, ARDS.
• Hemophagocytic lymphohistiocytosis (HLH) in severe cases.

Key differentials

• Other arboviral / febrile thrombocytopenia: chikungunya (more arthralgia, less leak/shock), Zika (rash, conjunctivitis, microcephaly in congenital).
• Malaria (P. falciparum) — periodic fever, splenomegaly, smear/RDT positive.
• Enteric fever — relative bradycardia, rose spots, less marked thrombocytopenia.
• Leptospirosis — conjunctival suffusion, jaundice, myalgia (calf), AKI.
• Scrub typhus — eschar, regional lymphadenopathy; responds to doxycycline.
• Sepsis / meningococcaemia, and in infants, other viral exanthems.

Feature	Dengue	Chikungunya	Malaria
Vector	Aedes (day)	Aedes (day)	Anopheles (night)
Hallmark	Plasma leak, low platelets	Severe arthralgia	Periodic fever, anaemia
Shock	Yes (DSS)	Rare	(severe falciparum)
Test	NS1/IgM	IgM/PCR	Smear/RDT

Prevention & vaccine

• Vector control is the mainstay — eliminate breeding sites, day-time bite protection.
• Dengvaxia (CYD-TDV) — live attenuated tetravalent vaccine; given only to seropositive (previously infected) children ≥ 9 years because in seronegative recipients it can act like a primary infection and increase risk of severe dengue on natural exposure (ADE concern). Newer vaccine Qdenga (TAK-003) is in wider use internationally.

Recently asked / exam angle

• "Best investigation in the first 5 days" → NS1 antigen. After day 5 → IgM ELISA.
• A child in shock whose HCT drops after fluids → internal/concealed bleeding → transfuse blood, not more saline.
• Platelet transfusion indicated only when < 10,000 or active bleeding; not for a number alone.
• Shock appears at defervescence, not at peak fever — the "critical phase" question.
• Narrow pulse pressure (≤ 20 mmHg) = the earliest sign of DSS in a child with maintained systolic BP.
• Tourniquet test positive = ≥ 10–20 petechiae/inch²; first manifestation in DHF grade I.
• Aspirin/NSAIDs are contraindicated; paracetamol is the antipyretic of choice.
• AST > ALT in dengue hepatitis; AST ≥ 1000 is a severe-dengue criterion.
• "White islands in a sea of red" convalescent rash.
• Secondary infection + ADE → severe dengue; IgG rises early in secondary infection.

Rapid revision

1. DENV is a Flavivirus, 4 serotypes; spread by day-biting Aedes aegypti; incubation 4–7 days.
2. Two pathologies: plasma leakage (→ shock, rising HCT) and bleeding (thrombocytopenia + platelet dysfunction).
3. Three phases: febrile (1–3) → critical (4–6) → recovery (7+); shock occurs in the critical phase at defervescence.
4. Warning signs (ABCD-L-M): abdominal pain, bleeding, fluid accumulation, drowsiness, liver > 2 cm, rising HCT + falling platelets, persistent vomiting → admit.
5. NS1 antigen = test of choice day 1–5; IgM ELISA after day 5; IgG early & high in secondary infection.
6. Haematocrit is the key monitoring tool: ≥ 20% rise = leak, sudden fall = bleed or recovery.
7. Resuscitate DSS with isotonic crystalloid bolus 10–20 mL/kg, escalate to colloid; titrate to HCT and urine output (~0.5 mL/kg/hr).
8. HCT falling + still in shock = concealed bleed → transfuse blood.
9. Platelets: transfuse if < 10,000 or active bleeding; maintain > 50,000 pre-procedure; no prophylactic transfusion.
10. Narrow pulse pressure ≤ 20 mmHg is the cardinal early sign of paediatric dengue shock.
11. Avoid aspirin/NSAIDs/IM injections; use paracetamol. Stop IV fluids in convalescence to prevent fluid overload.
12. Dengvaxia only in seropositive children ≥ 9 yr; severe dengue driven by ADE in secondary heterologous infection.