What are the diagnostic and treatment steps for a patient with a suspected dengue infection, as indicated by the presence of Non-Structural protein 1 (NS1) antigen?

Management of Trace Dengue NS1 Antigen Result

A trace NS1 antigen result should be interpreted as positive for acute dengue infection and managed identically to a clearly positive NS1 result, with immediate clinical assessment for warning signs, supportive care, and close monitoring during the critical phase (days 4-6). 1

Diagnostic Interpretation of Trace NS1

• Treat trace NS1 results as positive confirmatory evidence of acute dengue infection, as NS1 antigen is detectable as early as day 1 of symptom onset and remains positive during the first week of illness. 1, 2

• NS1 antigen is secreted from infected host cells and can remain detectable for up to 10 days after symptom onset, with highest detection rates during the acute phase. 3

• The sensitivity of NS1 detection is inversely proportional to the presence of IgG antibodies—secondary dengue infections may show lower NS1 levels or trace results due to rapid antibody-mediated viral clearance. 4, 5

• A trace result likely reflects lower viral antigen levels but still confirms active infection requiring full clinical management. 5

Immediate Clinical Assessment

Assess immediately for WHO warning signs that indicate potential progression to severe dengue: 1

• Severe abdominal pain or tenderness
• Persistent vomiting (≥3 episodes in 24 hours)
• Clinical fluid accumulation (pleural effusion, ascites)
• Mucosal bleeding (epistaxis, gingival bleeding, hematemesis)
• Lethargy or restlessness
• Liver enlargement >2 cm
• Rising hematocrit concurrent with rapid platelet decline

Risk Stratification and Management Pathway

For patients WITHOUT warning signs: 1

• Provide supportive care with adequate oral hydration (maintenance fluids plus deficit replacement)
• Use acetaminophen for fever control (avoid NSAIDs and aspirin due to bleeding risk)
• Obtain baseline complete blood count with platelet count and hematocrit
• Arrange daily monitoring during days 3-7 of illness
• Provide clear patient education on danger signs requiring immediate return

For patients WITH warning signs: 1

• Hospitalize immediately for intravenous fluid resuscitation and intensive monitoring
• Initiate crystalloid fluid therapy with close monitoring of hematocrit and vital signs
• Monitor for plasma leakage (rising hematocrit >20% indicates impending severe dengue)
• Increase monitoring frequency to every 1-4 hours depending on clinical status

Critical Phase Monitoring (Days 4-6)

The critical phase typically occurs around days 4-6 when plasma leakage and severe complications develop—patients require heightened surveillance during this window regardless of initial NS1 level. 1

• Monitor hematocrit and platelet count daily (or more frequently if hospitalized)
• A rising hematocrit >20% from baseline indicates plasma leakage and impending severe dengue 1
• Watch for rapid platelet decline, especially when dropping below 50,000/μL
• Assess for signs of shock: cold extremities, delayed capillary refill, narrow pulse pressure, hypotension

Laboratory Monitoring Schedule

• Baseline testing: Complete blood count with differential, hematocrit, platelet count 1
• Outpatient monitoring: Daily CBC during days 3-7 of illness 1
• Hospitalized patients: CBC every 4-12 hours depending on clinical severity 1
• Consider liver function tests and coagulation studies if bleeding manifestations present

Patient Education on Danger Signs

Instruct patients to return immediately for: 1

• Severe or persistent abdominal pain
• Persistent vomiting preventing oral intake
• Any bleeding (nosebleeds, bloody vomit, blood in stool, heavy menstrual bleeding)
• Altered mental status, confusion, or extreme lethargy
• Cold or clammy extremities
• Decreased urine output or no urination for >6 hours
• Difficulty breathing or rapid breathing

Follow-up Strategy

• Schedule follow-up within 24-48 hours for outpatients without warning signs 1
• Provide written instructions for daily self-monitoring with clear return precautions 1
• Consider earlier follow-up (12-24 hours) if patient presents on day 3-4 of illness, as they are approaching the critical phase

Common Pitfalls to Avoid

• Do not dismiss trace NS1 results as insignificant—they confirm acute infection requiring full dengue management protocols 3, 5
• Do not base hospitalization decisions solely on NS1 positivity or trace levels—clinical warning signs determine disposition, not laboratory test intensity 1
• NS1 positivity beyond day 5 of illness is associated with higher risk of severe dengue (odds ratio 3.0), warranting closer monitoring 6
• False-negative NS1 results can occur in secondary infections due to rapid antibody responses, so negative results do not exclude dengue 4, 5
• Never use NSAIDs or aspirin for fever control due to increased bleeding risk—acetaminophen is the only appropriate antipyretic