What are the phases of dengue?

Phases of Dengue

Dengue follows a characteristic triphasic clinical course consisting of the febrile phase (days 1-3), critical phase (days 4-6), and recovery phase (day 7 onwards), with the critical phase representing the period of highest risk for progression to severe dengue and shock. 1

The Three Clinical Phases

Febrile Phase (Days 1-3)

• This initial phase presents with acute onset of fever, frontal headache, retro-orbital pain, myalgia, arthralgia, and rash, typically occurring 4-8 days after mosquito exposure 2, 3
• Dengue virus RNA can be detected in serum from approximately 2 days before to 1 week after illness onset, making PCR/NAAT testing most effective during this early period 4
• NS1 antigen detection is particularly useful during the febrile phase, detectable from day 1 to day 10 after symptom onset 2
• During the first 3 days of illness, key prognostic indicators for severe disease include platelet count ≤100,000/mm³ and serum albumin <35 g/L 5
• Most dengue infections (>90%) remain mild during this phase, but early identification of warning signs is crucial 1

Critical Phase (Days 4-6)

• The critical phase typically coincides with defervescence and represents the period when plasma leakage, hemorrhagic manifestations, and shock are most likely to occur 2, 6
• Warning signs that emerge during this phase include persistent vomiting, abdominal pain/tenderness, clinical fluid accumulation (ascites, pleural effusion), mucosal bleeding, lethargy/restlessness, hepatomegaly, and rising hematocrit with concurrent thrombocytopenia 2, 3
• Laboratory abnormalities become more pronounced: significantly lower white blood cell and platelet counts, higher hematocrit, and elevated AST and ALT values compared to the febrile phase 6
• From days 4-6, prognostic indicators for severe disease include AST >400 U/L, ALT >400 U/L, albumin <35 g/L, and total bilirubin >17 μmol/L 5
• Dengue shock syndrome is characterized by systolic blood pressure <90 mmHg for >30 minutes or pulse pressure <20 mmHg, with signs of end-organ hypoperfusion 2
• Early recognition and appropriate fluid management during this phase can reduce case-fatality rates to <0.5% 2

Recovery Phase (Day 7 Onwards)

• This phase is marked by gradual reabsorption of extravasated fluids and clinical improvement 1
• Patients typically show resolution of fever, improvement in symptoms, stabilization of hemodynamic parameters, and normalization of laboratory values 3
• However, symptom persistence is common: approximately 55.7% of patients continue to have dengue-related symptoms 1 month after fever onset, with pain and dermatological manifestations being most frequent 7
• A small proportion (0.6%) of patients can develop severe dengue even during the WHO-proposed recovery phase, highlighting the need for continued vigilance 6

Clinical Implications by Phase

Diagnostic Testing Strategy

• During the febrile phase (≤7 days from symptom onset), nucleic acid amplification tests (NAATs) on serum should be performed 3, 8
• IgM antibody testing becomes appropriate after the first week of illness, typically during the critical or recovery phases 4, 2
• IgM antibodies develop during the first week of illness and can persist for months, with 87% of patients showing detectable IgM >60 days after symptom onset 4

Risk Stratification Considerations

• Secondary dengue infections (versus primary infections) carry higher risk of severe disease across all phases 9
• Elderly patients (≥65 years) demonstrate lower frequency of classical dengue symptoms during the febrile phase but face significantly higher risk of severe dengue in both febrile and critical phases 6
• Pre-existing comorbidities including diabetes, hypertension, renal disease, and cardiovascular disease increase risk of progression to severe disease 9

Common Pitfalls

• Narrow pulse pressure (<20 mmHg) is an earlier and more sensitive indicator of dengue shock than absolute hypotension and should be monitored closely during the critical phase 2
• Over-resuscitation with fluids during the critical phase can worsen outcomes given the underlying plasma leakage pathophysiology 2
• Aspirin and NSAIDs must be avoided throughout all phases due to increased bleeding risk and platelet dysfunction 3, 8