Dengue Infection in Adults (Third Edition) – Comprehensive Study Notes

Epidemiology

• Dengue is a major arthropod-borne viral disease with high morbidity/mortality, globally in tropical and subtropical regions; Malaysia experiencing increasing incidence.

• Malaysia (2000–2014): dengue incidence rose from 32 to 361 cases per 100,000 population.

• CFR target in Malaysia: < 0.2%. CFR decreased from 0.6% (2000) to 0.2% (2014).

• Most deaths occur in age 15 years and above. Urban areas (70–80% of cases) predominate due to high density and rapid development.

Dengue virus and serotype trends in Malaysia

• Dengue virus is a mosquito-borne flavivirus transmitted by Aedes aegypti and Aedes albopictus.

• Four distinct serotypes: DENV-1, DENV-2, DENV-3, DENV-4.

• Infection confers lifelong immunity to the homologous serotype but only partial/temporary protection against others.

• Secondary infection with a non-dominant serotype is a major risk factor for severe dengue due to antibody-dependent enhancement (ADE). Other contributors include viral virulence, host genetics, T-cell activation, viral load, and auto-antibodies.

• In Malaysia all four serotypes can co-circulate; a given serotype can predominate for about two years before replacement. In 2013–2014, predominant serotype shifted from DENV-2 to DENV-1 (Feb 2014 and Jun 2014).

Clinical manifestations and pathophysiology

3.1 Spectrum of dengue infection

• Incubation: typically 4–7 days (range 3–14 days).

• Disease spectrum: may be asymptomatic or range from undifferentiated febrile illness to severe dengue with plasma leakage and organ impairment.

• Dengue is systemic and dynamic; clinical, hematologic, and serologic profiles evolve day by day, especially during the critical phase (plasma leakage).

3.2 Clinical course of dengue infection

• Three phases: febrile, critical, recovery (see Fig. 5 reference).

• i) Febrile phase: fever high-grade, abrupt onset; lasts 2–7 days. Associated features: facial flushing, rash, myalgias, vomiting, headache; sore throat and injected pharynx may occur; conjunctival injection; mild mucosal bleeding (petechiae, mucosal). Possible per-vaginal bleeding in females; GI bleeding not uncommon. Tender liver may indicate warning signs. Early laboratory abnormality: leukopenia with progressive thrombocytopenia.

• ii) Critical phase: often after day 3 of fever (around defervescence) with rapid temperature drop. Marked increase in capillary permeability in some patients leading to plasma leakage; deterioration may occur despite fever abatement. Plasma leakage can cause compensated or decompensated shock and organ dysfunction. Warning signs: abdominal pain, persistent vomiting/diarrhoea, restlessness, altered consciousness, clinical fluid accumulation, mucosal bleeding, tender liver. Organ dysfunctions (hepatitis, encephalitis, myocarditis) can occur. Hemoconcentration (raised hematocrit) correlates with plasma volume loss; interpretation may be confounded by bleeding, aggressive fluid therapy, or haemodilution.

• iii) Recovery/reabsorption phase: plasma leakage stops around 24–48 h; reabsorption begins; patient improves, appetite returns; HCT stabilises then falls due to haemodilution; WBC recovers before platelets; rash may appear as a pattern described as 'islands of white in a sea of red' with pruritus. In some cases organ dysfunction may worsen during reabsorption.

• Haematologic changes: thrombocytopenia; leukopenia; hemoconcentration during leakage; transaminase elevations (AST often higher than ALT); hypoalbuminaemia and hypoproteinaemia common. HCT is a useful marker of plasma leakage but interpretation is influenced by shedding, bleeding, or fluid shifts.

3.3 Pathophysiology of plasma leakage in severe dengue infection

• Primary abnormality: acute increase in vascular permeability leading to plasma leakage into the extravascular space, causing hemoconcentration and hypovolaemia/shock.

• Consequences: reflex tachycardia, vasoconstriction, organ hypoperfusion;

  • Skin: cool, pale, delayed capillary refill

  • Cardiovascular: raised diastolic BP, narrowed pulse pressure

  • Renal: reduced urine output

  • GI: persistent vomiting/diarrhoea, abdominal pain

  • CNS: lethargy, restlessness, reduced consciousness

  • Respiratory: tachypnea

• If hypovolaemia is not corrected promptly, progression to refractory shock may occur; lactic acidosis may worsen myocardial function. Late-stage complications: massive bleeding, DIC, multi-organ failure.

• Immunopathology: abnormal immune response with cytokines/chemokines; T-cell activation; endothelial dysfunction. Elevated mediators include C3a, C5a, TNF-α, IL-2/6/10, IFN-α, histamine. ADE with heterotypic infection increases risk of severe dengue.

• Continuum of pathophysiology described as stages from normal circulation to compensated then decompensated (hypotensive) shock, with clinical and laboratory correlates (Table 1).

3.4 WHO classification

• Based on 1997 WHO scheme; distinguishing feature: plasma leakage in DHF; early febrile phase can overlap between DF and DHF.

• Limitations of 1997 classification: shock without full criteria for DHF, severe organ impairment without shock, and inadequate coverage of disease spectrum.

• WHO 2009 classification addresses severity levels more practically for management: DF (dengue fever), DHF (dengue hemorrhagic fever), DSS (dengue shock syndrome) with gradations.

3.5 Diagnostic challenges

• Clinical features are non-specific and overlap with other febrile illnesses; high index of suspicion and thorough history is essential (e.g., exposure in hotspots or clusters).

• Co-infections possible; organ dysfunction may be due to dengue or other etiologies; laboratory confirmation is essential for definitive diagnosis.

Disease notification

• Suspected dengue cases must be notified by telephone/fax/e-notification within 24 hours of diagnosis, followed by written notification using standard format.

• Delays increase transmission risk; notify changes in severity or death.

• Since 2014, all registered dengue cases must be laboratory-confirmed; all dengue deaths must be notified and investigated by District/Epidemiology Officers. Dengue mortality audit should be conducted within 7 days at hospital and state levels, chaired by Hospital Director and State Health Director.

• Guidelines compliance with Director General of Health Malaysia Circular No.15/2010.

Investigations

5.1 Disease monitoring tests

• White cell count (WCC) and platelet count: early febrile phase often normal; progresses to decreased WCC and platelets; no consistent correlation between platelet count and severity; serial monitoring important.

• Haematocrit (HCT): rising HCT indicates plasma leakage; baseline percentile values for Malaysian population discussed; normal ranges provided for gender/age categories.

• Other tests: liver function tests (LFT), renal profile (RP), coagulation profile, lactate, blood gases; troponin/CK discussed with specialists if myocarditis or rhabdomyolysis suspected.

• Recommendation: establish baseline HCT and WCC on first visit; serial monitoring as disease progresses.

5.2 Diagnostic tests

• Diagnostic tests include point-of-care NS1 antigen tests and rapid combo tests (NS1 + IgM/IgG), ELISA for NS1 and antibodies (IgM/IgG), RT-PCR for dengue genome, and viral isolation in specialized labs.

• Ideal test characteristics: differentiate dengue from other diseases, detect in acute stage, rapid results, inexpensive, easy to use; results should be interpreted in clinical context.

• Rapid Combo Test (RCT): detects virus and antibodies; read within manufacturer’s recommended window; sensitivity/specificity around ~93.9%/92% in some studies; useful early (viraemia) and later (antibody rise) phases.

• NS1 antigen ELISA: useful in acute infection; higher sensitivity in primary infection (75–97%) than secondary (60–70%); detection wanes after day 4–5 of illness; NS1 detection after day 5 may predict severe dengue.

• Dengue IgM ELISA: rises after day 5; primary infection IgM detectable in ~80% after day 5; most cases detectable by day 6–10; in secondary infections IgM may be lower/titled and may be undetectable if IgG dominates.

• Dengue IgG: detectable in 100% of patients after day 7 in primary/secondary infections; useful to differentiate secondary infection when high IgG is present. Repeat testing recommended if IgM negative after day 7.

• Differentiation of primary vs secondary infection: significant IgG elevation by ELISA indicates secondary infection; there are commercial kits with thresholds (e.g., PanBio cut-off) to indicate secondary infection.

• Serology false positives: cross-reactivity with other flaviviruses (e.g., JEV), malaria, leptospirosis, toxoplasmosis; connective tissue diseases.

• Dengue viral RNA detection (Real-time RT-PCR): detectable during viraemic stage up to ~days after onset; can determine circulating serotypes; limited to specialized centers due to cost and logistics.

• Virus isolation: available in select centers for research/surveillance/genotyping; Appendix 4 details sample collection.

• Overall laboratory confirmation requires multiple targets; Appendix 5–7 summarize lab guidance and interpretation.

Post-mortem investigations (Appendix 6)

• For dengue-related deaths, suitable samples for virus isolation and PCR include liver (best sample) and CSF if encephalitis; samples should be kept cold and transported to IMR or National Public Health Laboratory.

Management of dengue infection

7.1 Outpatient management

• Aim: symptomatic and supportive care; daily evaluation according to clinical phase (febrile, critical, reabsorption).

• Outpatient dengue monitoring record (Appendix 7) should be provided; primary care without POCT should refer to nearest health facility for monitoring.

• Point-of-care testing (RCT or NS1) recommended when dengue suspected.

• If admission indicated (Table 4 criteria): stabilize prior to transfer; communicate with receiving facility; if not admitted, daily follow-up from day 3 onwards until afebrile for at least 24–48 hours without antipyretics.

• Provide Home Care Leaflet (Appendix 9).

7.2 Patient triaging at emergency and outpatient department

• Purpose: identify patients needing urgent attention; triage checklist includes fever history, abdominal pain, vomiting, dizziness, bleeding; monitor mental state, BP, capillary refill, respiratory rate.

7.3 Criteria for hospital referral/admission

• Referral from primary care: consider warning signs, dehydration, shock, organ failure, comorbidities, pregnancy, social factors; rising HCT with falling platelets.

• Referral from hospitals without specialists to those with specialists: consult nearest physician for severe dengue, pregnancy, and comorbidity cases; pre-transfer optimization and information transfer required.

• Emergency department interventions: rapid reassessment; immediately perform required tests (FBC, HCT, POCT NS1/RCT, ABGs, LFT/RP, CK); imaging (CXR, ultrasound) to evaluate vascular leakage; do not delay admission.

7.3.4 Laboratory tests in ED

• Immediate tests: FBC and HCT; POCT NS1/RCT; in suspected severe dengue, blood gases, serum lactate, LFT, RP, CK; troponin/CKMB if myocarditis suspected.

7.3.5 Imaging in ED for admitted patients

• Chest x-ray and ultrasound to assess vascular leakage; ultrasound can assess third-space fluid (pleural effusion, pericardial effusion, gallbladder wall edema, intraperitoneal fluid); IVC collapsibility as indirect fluid status indicator.

7.3.6 Recommendation 4 and 7.3–7.3.5 highlights

• Dengue assessment checklist (Appendix 8) should be filled for all suspected dengue cases.

• All admitted dengue patients require fluid therapy (oral or IV) and ongoing monitoring; IV fluid adjustments based on clinical status.

• Deteriorating patients require uptriage and escalation to higher care.

7.4 Disease monitoring

• Principles: during critical phase, monitor closely and adjust fluids; identify onset of reabsorption to taper IV fluids.

• Inpatient monitoring: use Dengue Assessment Checklist (Appendix 8) and Inpatient Dengue Monitoring Chart (Appendix 10); frequency and parameters summarized in Tables 5–6.

• Table 5 (summary by phase): febrile (differentiation from other febrile illnesses), critical (plasma leakage and possible organ dysfunction), reabsorption (cessation of leakage; risk of fluid overload if IV fluids continued).

• Table 6 (frequency of monitoring): vital signs and laboratory tests every 4–6 hours in the febrile/critical phases; in shock, more frequent (15–30 min until stable, then 1–2 hourly); repeated FBC, HCT, LFT, RP, lactate, ABG, CK, electrolytes as clinically indicated; imaging as indicated.

7.5 Fluid management

• 7.5.1 Non-shock patients (DF with warning signs)

  • Common pitfalls: over-reliance on HCT or isolated signs; prolonged fixed fluid regime; continuing IV fluids during recovery; over-resuscitation in comorbid patients.

  • For non-shock dengue with maintained oral intake: encourage oral fluids; if ongoing plasma leakage (increasing HCT with dehydration signs), initiate IV crystalloids.

  • Recommended maintenance IV rate for non-obese adults: $ext{Maintenance fluid rate} \approx 1.2 ext{ to } 1.5 \, \frac{\text{mL}}{\text{kg} \cdot \text{hour}}$

  • In patients with persistent vomiting or inability to tolerate oral fluids, or severe diarrhoea, IV fluids may be required with careful dose adjustments.

  • If HCT rising with ongoing leakage despite oral intake, consider graded fluid bolus with close monitoring (Table 8).

  • Target urine output: $0.5 \text{ to } 1.0 \, \mathrm{mL/kg/hour}.$

  • Recovery phase: reduce IV fluids as leakage stops; monitor for signs of fluid overload.

• 7.5.2 Dengue Shock Syndrome (DSS)

  • DSS is a medical emergency; recognize compensated shock early and treat promptly. All dengue shock cases should be managed in HDU/ICU. Do not delay fluid resuscitation awaiting ICU admission.

  • Initial resuscitation: consider crystalloids or colloids; trial has shown no clear superiority of colloids in DSS over crystalloids; colloids may be preferred in refractory shock, but prolonged use as maintenance fluid should be avoided.

  • Crystalloids vs colloids: typical bolus approach and subsequent maintenance guided by response; colloids include gelatin or hydroxyethyl starch (HES) with caution due to potential adverse effects in liver/renal function and coagulation. 4% albumin not conclusively superior; hypertonic saline/lactate-based solutions have limited data.

  • Recommended initial approach (Algorithm A): 5–10 mL/kg/h isotonic crystalloid for 1 hour; reassess; if still unstable, 10–20 mL/kg/h for 1–2 hours; monitor HCT; if HCT remains high or there is occult bleeding, escalate to second bolus or switch to colloid; after stabilization, taper fluids over 24–48 hours.

  • If persistent shock despite two cycles of resuscitation and high HCT, suspect occult/overt bleeding; proceed with transfusion as indicated (see below).

  • If HCT does not decrease with resuscitation or shock persists, consider alternative causes (sepsis, cardiac dysfunction, cytokine storm, liver failure, AKI, drug effects).

  • Algorithm B (decompensated shock): administer 20 mL/kg bolus of colloid/crystalloid within 15–30 minutes; reassess; follow with maintenance fluids and vasopressors as needed.

  • Algorithm C (decompensated shock with bleeding & leaking): manage bleeding while treating shock; use echocardiography/non-invasive cardiac output monitoring to tailor therapy; consider OGDS for GI bleeding; transfuse blood products as needed.

  • Monitoring response: use Caval index (
    IVC collapsibility) to assess volume status; Caval index = (IVCexp - IVCinsp) / IVC_exp × 100%. A higher index suggests fluid responsiveness; should be interpreted by trained clinicians in context.

• 7.5.3 Principles for fluid resuscitation

  • Initial and subsequent volumes depend on degree of shock; titrate to clinical response to maintain perfusion and avoid fluid overload.

  • Fluid responsiveness parameters include clinical, laboratory, and imaging indicators (see Table 9 in the guideline): clinical improvement, capillary refill, BP/pulse pressure improvements, urine output, lactate clearance, ABG improvements, and ultrasound indices (IVC collapsibility).

  • Avoid aggressive crystalloids beyond 48 hours of plasma leakage unless clinically indicated; consider transitioning to maintenance/deficit-limited therapy as patient stabilizes.

• 7.5.4 Metabolic acidosis

  • Shock may occur with normal BP due to slow leakage; compensated metabolic acidosis is an early sign of shock.

  • Lactic acidosis reflects tissue hypoperfusion; lactate clearance is a useful therapy-guiding parameter; aim for lactate clearance of at least 20% within 2 hours.

  • ABG: monitor base excess, bicarbonate, CO2; respiratory alkalosis/metabolic acidosis patterns may be seen in liver failure, encephalopathy, and sepsis.

• 7.5.5 Arterial blood gases (ABG)

  • ABG is used 2–4 hourly in shock for detection of worsening acidosis.

  • Common patterns: mixed respiratory alkalosis with metabolic acidosis; hypoxaemia may indicate fluid overload/pleural effusion/edema.

• 7.5.6 Electrolyte and acid-base imbalances

  • Monitor sodium (hyponatraemia common in severe dengue), calcium, phosphate, magnesium.

• 7.6 Management of complications in dengue infection

  • 7.6.1 Bleeding/haemostasis

  • Haemostatic abnormalities stem from endothelial activation; thrombocytopaenia and coagulation abnormalities do not reliably predict bleeding. Markers of endothelial activation (thrombomodulin, tissue factor, VWF) are higher in severe dengue.

  • Significant bleeding is defined by hemodynamic instability; non-mucosal bleeding and minor bleeding often self-limited. Occult bleeding suspected if HCT fails to rise as expected with adequate fluid replacement (40–60 mL/kg) or if there is progressive acidosis.

  • Transfusion strategy: transfusion of packed red blood cells (PRBC) and/or blood components indicated for significant bleeding. Prophylactic transfusion in dengue (platelets/FFP) is not routinely recommended; endoscopy for persistent UGIB; endoscopic therapy for ulcers if needed; recombinant activated factor VII not routinely recommended.

  • 7.6.2 Hepatitis in dengue

  • Clinical features: abdominal pain, nausea/vomiting, hepatomegaly, transaminases elevated (AST often higher than ALT; >10x normal in some cases).

  • Pathogenesis: virus effects, immune-mediated injury, hypotensive/ischaemic injury, drug hepatotoxicity.

  • NAC as treatment for dengue-related hepatitis has insufficient evidence; use is controversial; supportive care remains main approach; consider NAC regimens only in specific contexts.

  • 7.6.3 Cardiac complications

  • Dengue may cause myocarditis, arrhythmias, myocardial depression. Suspect in refractory shock; perform ECG, cardiac biomarkers, echocardiography.

  • Management focuses on cautious fluid resuscitation to maintain perfusion; antivirals/immunomodulators not proven; inotropes/vasopressors may be used temporarily or for cardiogenic shock with guidance from imaging/biomarkers.

  • 7.6.4 Neurological complications

  • Spectrum: encephalopathy, encephalitis, intracranial haemorrhage, meningitis/encephalitis; immune-mediated conditions (ADEM, GBS, myelitis, myositis, ophthalmic manifestations).

  • Encephalopathy is common and may result from shock/hypoxia/edema; dengue encephalitis presents with fever, headache, seizures, altered consciousness after 5–7 days; CSF may be normal or show pleocytosis; MRI is preferred but not always diagnostic.

  • Management is supportive; corticosteroids/IVIg/plasmapheresis have limited/unclear evidence; treat raised ICP if present.

  • 7.6.5 Renal complications

  • Dengue can cause transient proteinuria/haematuria; ARF may occur due to hypotension, haemolysis, DIC, rhabdomyolysis; management includes fluids, electrolytes, dialysis if indicated; peritoneal dialysis is not recommended due to bleeding risk.

  • 7.6.6 Haemophagocytic syndrome (HLH/HPS)

  • Rare but fatal; characterized by high ferritin, cytopaenias, coagulopathy, hypertriglyceridaemia, and multi-organ involvement; diagnosis via HLH-2004 criteria or HScore; mainstay is supportive care; high-dose steroids with/without IVIg may help in severe cases; treat underlying triggers.

7.7 Intensive care management of dengue infection

• ICU management follows general critical care principles; indications for ICU referral are organ-system specific (respiratory, cardiovascular, neurologic, GI, haematologic, renal).

• Respiratory support: non-invasive ventilation can be beneficial in alert, cooperative patients; intubation carries increased risk due to haemodynamics and potential bleeding; aim to minimize airway pressures to prevent reduced venous return.

• Haemodynamic support: fluids are central; vasopressors/inotropes used transiently to maintain MAP while optimizing fluid status; norepinephrine is preferred in septic shock; dobutamine may be added in cardiogenic shock; avoid CVP-guided fluid management as a routine guide.

• Renal replacement therapy (RRT) may be needed for severe AKI.

• Invasive procedures safety: CVC insertion should be performed with precautions; avoid routine prophylactic platelets/FFP; real-time ultrasound guidance is recommended; avoid subclavian approach due to compression risk; avoid routine CVP guidance for fluid management.

• Other invasive procedures should be used judiciously given bleeding risk; nasogastric tubes should be careful in bleeding disorders; gastric tube use may be considered with caution; pleural taps/chest drains should be avoided if possible due to bleeding risk.

Dengue infection in pregnancy

• Pregnancy alters dengue management due to physiological changes (elevated HCT masked by haemodilution; baseline BP lower; tachycardia and liver enzyme changes).

• Outcomes: higher risk of DSS and severe dengue; maternal and fetal complications include abortion, preterm birth, fetal distress, and higher mortality; mode of delivery generally spontaneous; crossmatch and blood products ready for obstetric interventions; placenta transfer and neonatal infection possible; neonatal monitoring for up to one week if congenital dengue suspected.

• Multidisciplinary care required (physician, anaesthetist, obstetrician).

Discharge criteria

• Criteria to discharge: improved general well-being; afebrile for 24–48 h; rising WCC followed by platelets; stable haematocrit; resolution/recovery of organ dysfunction.

Vaccination and supplements

• Dengue vaccines: trials in pediatric populations; limited evidence for adults; not currently recommended for routine adults based on this guideline.

• Food and supplements (e.g., Carica papaya leaves, cactus extracts, etc.) have not proven benefits in preventing complications or improving outcomes; management focus remains plasma leakage and immune activation.

Prevention and implementation

• Prevention of dengue transmission in hospitals (nosocomial transmission): patients are viraemic during febrile phase; mosquito avoidance measures in hospitals are not robustly proven; community measures such as netting/repellents have more evidence.

• Implementation: standardised management across healthcare levels; dissemination of guidelines; training; audit indicators; resourcing for diagnostic tools and multidisciplinary dengue management teams.

Appendix and references (highlights)

• Appendix 1–6: Search strategy, clinical questions, WHO classifications, sample collection methods, diagnostic tests and interpretation, lab guidelines.

• Appendix 7–10: Outpatient monitoring record, dengue assessment checklist, home care leaflet, inpatient monitoring chart.

• References include WHO guidelines (2009), local MaHTAS guidelines (2015), and multiple peer-reviewed sources on dengue pathophysiology, management, and diagnostics.

Key numbers and formulas (for quick reference)

• Incubation period: $4-7 ext{ days}$ (range 3–14 days).

• Incidence in Malaysia: from $32$ to $361$ cases per 100,000 population (2000–2014).

• Case fatality rate target: <0.2\%; observed CFR reduced to 0.2% by 2014.

• Serotypes: $DENV-1, DENV-2, DENV-3, DENV-4$; lifelong homologous immunity; partial heterologous immunity; ADE risk with secondary infections.

• Phases of illness: febrile phase, critical phase (≈ 24–48 h), recovery/reabsorption phase.

• Hematocrit warning thresholds (Dengue assessment checklist Table 3):

  • Male < 60 years: Hct > 46\%

  • Male ≥ 60 years: Hct > 42\%

  • Female all ages: Hct > 40\%

• Fluids in non-shock dengue (maintenance): $1.2-1.5\ \text{mL/kg/hour}$ (adjusted for obesity via ABW).

• Nutrient/volume calculations for maintenance (non-obese): $ext{Maintenance} = 1.2-1.5 \frac{\text{mL}}{\text{kg}\cdot \text{hour}}$

• Graded IV bolus for non-shock with persistent leakage: 5 ml/kg/h for 1–2 h, then 3 ml/kg/h for 2–4 h, then 2 ml/kg/h or less.

• Graded IV bolus for DSS (initial resuscitation): 10–20 ml/kg as 1st/2nd bolus; subsequent steps based on response (Algorithm A/B/C).

• Caval index for IVC: $ext{Caval index} = \frac{IVC<em>{exp} - IVC</em>{insp}}{IVC_{exp}} \times 100\%$; higher values indicate fluid responsiveness (interpret with caution and imaging).

• Lactate clearance as a therapy-guiding metric: $ext{Lactate clearance} = \frac{\text{lactate}<em>{\text{initial}} - \text{lactate}</em>{\text{subsequent}}}{\text{lactate}_{\text{initial}}} \times 100\%$; ≥20\% within 2 hours is favorable.

• NS1 detection window: early acute phase; IgM rise after day 5; IgG detectable after day 7; RT-PCR detectable during viraemia (≈ day 0–5).