Dengue and other arboviral infections: Viva

Branch 1: Recognising the time-critical problem

The candidate should immediately recognise that this is dengue entering its critical phase. The travel history to a dengue-endemic country, the positive NS1 antigen, the defervescence of the fever with new abdominal pain and vomiting, and the rising haematocrit with a falling platelet count together meet WHO 2009 criteria for dengue with warning signs, and the magnitude of the haematocrit rise (25 per cent above baseline) signals significant plasma leak. The single most important teaching point is that the child is most at risk now, as the fever falls, not at the fever peak. [2]

The candidate should state the first priorities: airway, breathing and circulation; a fingerprick glucose; intravenous access; and a panel of baseline bloods including full blood count, electrolytes, liver function, albumin, coagulation and lactate. The disposition is admission for WHO group B management, because the warning signs and the haematocrit rise place her at risk of progression to severe dengue. [1]

Branch 2: Classification and the warning signs

The examiner will ask the candidate to reproduce the 2009 WHO classification. The candidate should describe the three categories (dengue without warning signs, dengue with warning signs, severe dengue) and list the seven warning signs: abdominal pain or tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy or restlessness, hepatomegaly greater than two centimetres, and a rising haematocrit with a falling platelet count. Severe dengue is reserved for plasma leakage causing shock or respiratory distress, severe bleeding, or organ impairment. [2]

The candidate should then classify this child as dengue with warning signs (abdominal pain, vomiting, and the haematocrit-platelet signature) and explain that a systematic review showed each of these warning signs roughly doubles the odds of progression to severe dengue, which justifies admission rather than outpatient care. [3]

Branch 3: Monitoring and the fluid decision

The examiner will probe the fluid strategy. The strong candidate states the defining principle: boluses are harmful in a stable child, and the goal is titrated isotonic crystalloid, not a preventive bolus. For group B management, 0.9 per cent saline or Hartmann's solution at 5 to 7 mL/kg per hour is started and titrated down as the haematocrit stabilises. The haematocrit is rechecked every six to twelve hours and the perfusion assessed hourly. [2]

The examiner will then ask what the candidate would do if the pulse pressure narrows below 20 mmHg. The correct answer is compensated dengue shock, managed with 10 to 20 mL/kg of isotonic crystalloid over one hour and reassessment before further fluid; repeated rapid boluses risk pulmonary oedema. Colloid is not first-line, steroids have no role, and prophylactic platelet transfusion is not indicated without bleeding. Aspirin and non-steroidal anti-inflammatories are contraindicated; paracetamol only. [2]

Branch 4: Recovery and discharge

The examiner will ask how the candidate recognises recovery. The candidate should describe the transition: the haematocrit falls, the pulse pressure widens, the appetite returns, and diuresis resumes. Intravenous fluids are tapered over 24 to 48 hours to avoid the recovery-phase complication of fluid overload, which presents as a gallop, tachypnoea and basal crackles. [2]

The discharge criteria are an afebrile child who is eating and drinking, passing urine, with a stable or falling haematocrit, a rising platelet count and a widened pulse pressure. The candidate should state that a platelet count that has not yet normalised is not a barrier to discharge in a clinically well child, and that the family is counselled that a future dengue infection with a different serotype carries a higher risk of severe disease. [2]

Branch 5: The vaccine question

The examiner will ask about dengue vaccine. The candidate should explain the two principal live-attenuated tetravalent vaccines. CYD-TDV (Dengvaxia) is recommended only for seropositive children because it increased hospitalisation in seronegative recipients, consistent with vaccine-mediated primary sensitisation and later antibody-dependent enhancement. TAK-003 (Qdenga) has good efficacy against DENV-1 and DENV-2 with waning DENV-3 protection and caution in seronegative individuals, which keeps the WHO recommendation measured. The candidate should be clear that no dengue vaccine is in routine use in ANZ and that prevention in non-endemic practice is travel advice, repellent and bite avoidance. [1]