Dengue Fever: Phases, Warning Signs and Fluid Management

Dengue is a viral infection spread by Aedes mosquitoes, mainly Aedes aegypti, which bite during the day. It causes large outbreaks in Pakistan and across South and Southeast Asia, especially after the monsoon. Most patients recover, but a small number develop severe dengue with plasma leakage and shock. Careful monitoring during the "critical phase" prevents most deaths.

The virus

There are four dengue virus serotypes. Infection with one gives lifelong immunity to that serotype only. A second infection with a different serotype carries a higher risk of severe dengue.

Phases of illness

1. Febrile phase (days 1–3):
   • sudden high fever
   • headache and pain behind the eyes
   • severe muscle and joint pain ("breakbone fever")
   • flushing and a rash
   • nausea
   • a positive tourniquet test
2. Critical phase (around days 3–7, as the fever falls): increased capillary permeability may cause plasma leakage, leading to:
   • a rising haematocrit
   • pleural effusion and ascites
   • shock
   The platelet count usually falls during this phase. This is the most dangerous period, even though the patient may seem better because the fever has gone.
3. Recovery phase:
   • leaked fluid is reabsorbed
   • appetite returns
   • the platelet count rises
   • a "convalescent" rash may appear
   Fluid overload is a risk if IV fluids are continued too long.

Warning signs (WHO)

Any of these means the patient needs hospital care and close monitoring:

• Abdominal pain or tenderness.
• Persistent vomiting.
• Clinical fluid accumulation (ascites, pleural effusion).
• Mucosal bleeding.
• Lethargy or restlessness.
• Liver enlargement of more than 2 cm.
• Rising haematocrit together with a rapid fall in platelet count.

Severe dengue

• Severe plasma leakage leading to shock (dengue shock syndrome) or fluid accumulation with respiratory distress.
• Severe bleeding.
• Severe organ involvement:
  • liver (very high transaminases)
  • brain (impaired consciousness)
  • heart
  • other organs

Diagnosis

• NS1 antigen or PCR during the first 5 days of illness.
• IgM antibody from about day 5 onwards.
• Full blood count: low white cells, falling platelets and a rising haematocrit. Repeat it daily or more often in the critical phase.
• Other tests: liver function and electrolytes. Ultrasound can detect fluid leakage early.

Management

• No specific antiviral treatment. Care is supportive.
• Paracetamol for fever and pain. Avoid aspirin, ibuprofen and other NSAIDs, because they increase the risk of bleeding.
• Oral fluids for patients without warning signs, with daily review and clear advice to return if warning signs appear.
• Warning signs or severe dengue: admission, with carefully titrated IV crystalloids guided by vital signs, urine output and haematocrit, following WHO or national protocols. Reduce fluids as the patient improves, to avoid overload.
• Platelet transfusion is not given routinely for a low count alone. It is reserved for significant bleeding, according to local guidelines.

Prevention

• Remove standing water where mosquitoes breed (containers, tyres, flower pots).
• Use repellents, long sleeves and nets, including during the day.
• Community control of mosquito breeding.
• Dengue vaccines exist, but eligibility rules differ between countries.

Exam pearls

• The danger period starts when the fever falls (defervescence).
• Rising haematocrit means plasma leakage. Falling haematocrit with instability suggests bleeding.
• Never give NSAIDs in suspected dengue.

For more on tropical fevers, see the infectious diseases part of the Medicine Companion.

Test yourself

5 exam-style single-best-answer questions. Choose your answer, then tap “Show answer”.

1. When is the most dangerous phase of dengue?

   1. After recovery
   2. Before the fever starts
   3. First 24 hours of fever
   4. After 3 weeks
   5. Around defervescence (about days 3–7)
   Show answer

   Answer: E. Around defervescence (about days 3–7)
   Plasma leakage and shock occur in the critical phase, as fever falls.

2. Which painkiller should be used for dengue fever?

   1. Aspirin
   2. Naproxen
   3. Ibuprofen
   4. Paracetamol
   5. Diclofenac
   Show answer

   Answer: D. Paracetamol
   Paracetamol is safe; NSAIDs and aspirin increase bleeding risk.

3. Best test on day 2 of illness:

   1. Malaria film only
   2. Widal test
   3. IgG antibody
   4. Blood culture
   5. NS1 antigen or PCR
   Show answer

   Answer: E. NS1 antigen or PCR
   NS1 and PCR detect the virus in the first 5 days; IgM appears later.

4. Rising haematocrit with a rapidly falling platelet count indicates:

   1. Lab error
   2. Recovery
   3. Dehydration from vomiting only
   4. Plasma leakage — a warning sign
   5. Bleeding only
   Show answer

   Answer: D. Plasma leakage — a warning sign
   This combination is a WHO warning sign of plasma leakage needing close monitoring.

5. Should platelets be transfused for a low count alone?

   1. Only in children
   2. Yes, below 150
   3. Always before discharge
   4. Yes, always below 100
   5. No, reserved for significant bleeding per guidelines
   Show answer

   Answer: E. No, reserved for significant bleeding per guidelines
   Prophylactic platelet transfusion for a low count without bleeding is not recommended.

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Disclaimer

For education and exam preparation only. This is not medical advice and must not be used to diagnose or treat patients. Always follow current clinical guidelines and the advice of qualified senior colleagues.