Dengue and other arboviral infections: Case

This boy has dengue with warning signs progressing to the plasma-leak critical phase. His travel to the Philippines without bite avoidance, the defervescence of his fever with new abdominal pain, vomiting and lethargy, the positive NS1 antigen, the 23 per cent rise in haematocrit over baseline, and the thrombocytopenia together meet WHO 2009 criteria for dengue with warning signs, and his narrowed pulse pressure of 26 mmHg with cool peripheries places him at the threshold of compensated shock. The clinical task over the next 24 to 48 hours is to escort him safely through the leak with titrated isotonic crystalloid. [2]

Clinical findings

The key findings are the warning signs (abdominal pain, persistent vomiting, lethargy), the haematocrit-platelet signature of leak (a haematocrit of 0.48 against a baseline of 0.39, platelets 58 x10^9/L), the mild hypoalbuminaemia of capillary leak, and the borderline perfusion with a narrowed pulse pressure. He is not yet in severe dengue by the strict criterion (pulse pressure remains above 20 mmHg and there is no organ impairment), but he sits at the boundary, so close monitoring and a clear escalation plan are essential. [1]

The candidate should articulate the problem representation clearly: a school-age returned traveller with dengue, defervescence, warning signs and a rising haematocrit, in WHO group B at risk of progression to severe dengue. This single statement tells the examiner the diagnosis, the classification, the severity and the plan. [3]

Investigations

The dengue NS1 antigen confirms infection in the first five days of illness, which is its most sensitive window. The full blood count shows the leak signature: a haematocrit 23 per cent above baseline, indicating significant haemoconcentration, and a platelet count well below 100 x10^9/L. Leucopenia and a relative lymphocytosis with atypical lymphocytes would be expected. [2]

The supporting panel is directed at severity: liver function (the albumin of 32 g/L confirms leak and a falling albumin is a marker of progression), coagulation, lactate, glucose, electrolytes and urea. A chest X-ray or bedside ultrasound is performed to look for an occult right pleural effusion, gallbladder wall thickening or ascites, which are early radiological signs of leak. Blood cultures are sent to exclude bacterial co-infection, which can coexist and confuse the shock picture. A lactate is a worthwhile addition, as it improved the prediction of severe dengue when added to the WHO warning signs in a Thai prospective cohort. [3]

Management

The management is WHO group B, and the defining principle is titrated isotonic crystalloid, not a prophylactic bolus. He is started on 0.9 per cent saline at 5 to 7 mL/kg per hour, and the rate is titrated down as the haematocrit stabilises and the perfusion improves. The haematocrit is rechecked every six to twelve hours and the pulse pressure, capillary refill, peripheral warmth, urine output and conscious level are assessed hourly. Aspirin and non-steroidal anti-inflammatories are contraindicated and paracetamol alone is used for any discomfort. [2]

If his pulse pressure narrows below 20 mmHg, he has moved to compensated dengue shock (group C), and the response is 10 to 20 mL/kg of isotonic crystalloid over one hour with reassessment before further fluid. Only for hypotensive shock is a faster 20 mL/kg bolus appropriate, with transfer to intensive care. Platelet and fresh-frozen plasma transfusion are reserved for active, clinically significant bleeding, not for the number alone; prophylactic platelet transfusion for thrombocytopenia without bleeding does not improve outcome. [2]

Recovery and discharge

Recovery is marked by a falling haematocrit, a widening pulse pressure, returning appetite and a diuresis. The critical error to avoid at this stage is failing to taper the intravenous fluid, which produces the recovery-phase complication of fluid overload: a gallop, tachypnoea, hypertension and basal crackles as extravascular fluid returns to the circulation. Intravenous fluids are tapered over 24 to 48 hours and stopped when the child is drinking well and the haematocrit is stable. [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 not yet back to normal is not a barrier to discharge in a clinically well child, and should give a written safety-net: return immediately if drowsiness, repeated vomiting, bleeding, abdominal pain or cold extremities develop. The family is counselled that a future dengue infection with a different serotype carries a higher risk of severe disease, so bite avoidance on any future travel remains important. [1]

Communication

The communication skill the exam rewards is a specific, written, behaviour-based safety-net delivered in plain language. The candidate should tell the family plainly that the dangerous part of dengue is the leak that comes as the fever settles, that the next day or two carry the highest risk, and exactly when to seek help. Offering the family the chance to repeat back the warning signs confirms understanding and is the single best protection against a late, fatal deterioration at home. [2]