🚨 "The end of the fever does not mean the end of the illness. With dengue fever, this is sometimes the most dangerous moment of all."
According to the World Health Organization (WHO), the number of dengue fever cases worldwide has risen almost 30-fold over the past 50 years.
In Vietnam, dengue fever remains one of the most common infectious diseases. According to the Ministry of Health, in 2024 the country recorded more than 114,900 cases and 18 deaths.
What is worrying is that many patients deteriorate not while the fever is high, but exactly when the fever begins to come down.
🔍 What is dengue fever?
Dengue fever is an acute infectious disease caused by the dengue virus, transmitted mainly through the bite of the striped Aedes mosquito.
Once it has entered the body, the dengue virus multiplies inside immune cells and sets off a complex inflammatory response. This process can alter the permeability of the blood vessel walls and affect the platelets, the clotting system and many vital organs in the body.
These changes can affect:
• The circulatory system
• The blood vessel walls
• Blood clotting function
• Platelets
• The liver, heart, brain and many other organs
Without timely monitoring and treatment, the patient may develop dangerous, life-threatening complications.
⚠️ What is happening inside the patient's body?
To understand why a patient can deteriorate even after the fever has come down, it helps to look at the changes taking place inside the body at each stage of the illness.
1. The high fever stage: the body is fighting the virus (Days 1–3)
During the first days of illness, the immune system works hard to control the dengue virus.
Patients commonly develop:
• A high fever of 39–40°C
• Severe headache
• Pain behind the eyes
• Aching muscles and joints
• Nausea and loss of appetite
• Prolonged tiredness
At this stage, blood tests may show the white blood cell and platelet counts starting to fall.
This is a sign that the body is being affected by the virus and needs close monitoring.
2. The critical stage: when the fever comes down (Days 3–7)
Many people believe that the end of the fever means the illness is over.
In reality, according to WHO, the CDC and infectious disease specialists, the period from day 3 to day 7 is when the risk of complications is highest.
At this point, the blood vessel walls become more permeable, allowing plasma to leak out of the circulation.
This phenomenon is known as:
🚨 Plasma leakage
It is not the virus that directly causes shock. The danger lies in plasma escaping from the blood vessels, which severely reduces the circulating volume.
This is the most important disease mechanism leading to dengue shock.
❗ How dangerous is plasma leakage?
When too much plasma leaks out:
• The blood becomes more concentrated
• The volume of circulating blood falls
• Blood pressure gradually drops
• The organs do not receive enough oxygen and nutrients
❤️ The heart has to work harder to compensate
The patient may develop:
• Severe or persistent abdominal pain
• Persistent vomiting
• Cold hands and feet
• Passing little urine
• Lethargy or unusual restlessness
• Exhaustion and difficulty standing steadily
• A drop in blood pressure
In severe cases, the patient may go into shock, develop multi-organ failure or die without prompt emergency care.
🩸 Why do patients bleed?
One of the common features of dengue fever is bleeding or haemorrhage.
The main causes include:
• A fall in the platelet count
• Disturbance of the blood clotting process
• Damage to the blood vessel walls
Patients may experience:
• Pinpoint bleeding spots under the skin
• Nosebleeds
• Bleeding gums
• Heavy or unusually prolonged menstrual bleeding
• Blood in the urine
More severe forms may include:
• Gastrointestinal bleeding
• Pulmonary haemorrhage
• Cerebral haemorrhage
These are all complications that need emergency treatment.
⚠️ It is important to note that not every patient with severe dengue fever develops obvious bleeding. Many cases become severe mainly because of plasma leakage and circulatory shock. Seeing no bleeding therefore does not mean the illness is mild or that the patient is out of danger.
🌱 The recovery stage: the body begins to repair the damage
If the critical stage is safely passed, the body gradually reabsorbs the fluid that has leaked out.
Patients usually show:
• A complete end to the fever
• Better eating and drinking
• Passing more urine
• Growing alertness and strength
• Platelets beginning to rise again
Even so, patients should still attend follow-up visits and be monitored as directed by their doctor to make sure recovery is complete.
⛔ Warning signs that call for an immediate hospital visit
If any of the following appear, the patient should be taken to a medical facility as soon as possible:
1. Severe or persistent abdominal pain
2. Frequent vomiting
3. Unusual bleeding
4. Cold hands and feet
5. Lethargy or difficulty waking
6. Difficulty breathing
7. Passing little urine
8. Tiredness that increases rapidly after the fever has come down
These may be warning signs of dengue shock or of a severe complication developing.
🛡️ What can be done to reduce the risk of complications?
• Monitor closely during the days when the fever is coming down
• Keep well hydrated with water, oresol or electrolyte solutions as advised by a health worker
• Attend follow-up visits and tests on schedule
• Do not give intravenous fluids at home on your own initiative
• Do not take aspirin or non-steroidal anti-inflammatory drugs without a doctor's instruction
• Go to hospital immediately if any warning sign appears
According to WHO, with early detection and correct treatment, the death rate from dengue fever can fall to below 1%.
📝 Conclusion
Dengue fever is not just an ordinary fever.
Inside the body, the dengue virus can lower the platelet count, damage the blood vessel walls, cause plasma leakage and bleeding, and affect many vital organs.
What is especially important to remember is that the most dangerous moment is usually not when the fever is high, but when the patient begins to have less fever.
With dengue fever, the fever may come down while the risk of complications has not passed. Close monitoring during days 3–7, early recognition of the warning signs and prompt medical attention are key to limiting severe complications and reducing the risk of death.
🏥 Some medical facilities offering dengue fever examination and treatment
When warning signs appear, or when the course of the illness needs monitoring, patients should attend a reputable medical facility for timely assessment and treatment.
📍 City International Hospital (CIH)
📍Hoan My Sai Gon Hospital
📍FV Hospital
📍Nam Sai Gon International General Hospital
📍Thu Cuc TCI Healthcare System
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References:
- World Health Organization (WHO)
- Ministry of Health of Vietnam
- Centers for Disease Control and Prevention (CDC)
- Central Children's Hospital
- Ho Chi Minh City University Medical Centre
- Vietnam Medical Journal
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