Dengue infection is a systemic and dynamic disease. It has a wide clinical spectrum that includes both severe and non-severe clinical manifestations. After the incubation period (interval between exposure to infection and appearance of first symptoms of the disease), the illness begins abruptly and is followed by the three phases -- febrile, critical and recovery.
For a disease that is complex in its manifestations, management is relatively simple, inexpensive and very effective in saving lives so long as correct and timely interventions are instituted.
The key is early recognition and understanding of the clinical problems during the different phases of the disease, leading to a rational approach to case management and a good clinical outcome. Activities (triage and management decisions) at the primary and secondary care levels (where patients are first seen and evaluated) are critical in determining the clinical outcome of dengue.
A well-managed front-line response not only reduces the number of unnecessary hospital admissions but also saves the lives of dengue patients. Early notification of dengue cases seen in primary and secondary care is crucial for identifying outbreaks and initiating an early response.
Patients typically develop high-grade fever suddenly. This acute febrile phase usually lasts 2-7 days and is often accompanied by facial flushing, skin redness, generalized body ache, muscle, joint pains and headache. Some patients may have sore throat, swelling and redness of the throat and the eyes.
More often, the initial diagnosis of physicians during initial consult is acute tonsillitis. Poor appetite, nausea and vomiting are common.
It can be difficult to distinguish dengue clinically from non-dengue febrile diseases in the early febrile phase. A positive tourniquet test in this phase increases the probability of dengue.
In addition, these clinical features are indistinguishable between severe and non-severe dengue cases. Therefore monitoring for warning signs and other clinical parameters is crucial to recognizing progression to the critical phase.
Mild hemorrhagic manifestations like skin rashes and mucosal membrane bleeding (e.g. nose and gums) may be seen. Massive vaginal bleeding (in women of childbearing age) and gastrointestinal bleeding may occur during this phase but is not common.
The liver is often enlarged and tender after a few days of fever. The earliest abnormality in the full blood count is a progressive decrease in total white cell count (WBC), which should alert the physician to a high probability of dengue.
Around the time when fever goes down, when the temperature drops to 37.5-38oC or less and remains below this level, usually on days 3-7 of illness, an increase in capillary (tinniest blood vessel) permeability (able to pass through or leakage) in parallel with increasing hematocrit (measured packed red cell volume of the blood) levels may occur. This marks the beginning of the critical phase. The period of clinically significant plasma leakage usually lasts 24-48 hours.
Progressive decrease of white blood count followed by a rapid decrease in platelet count usually precedes plasma leakage. At this point patients without an increase in capillary permeability will improve, while those with increased capillary permeability may become worse as a result of lost plasma volume.
The degree of plasma leakage varies. Fluid accumulation in the lungs and abdominal cavity may be clinically detectable depending on the degree of plasma leakage and the volume of fluid therapy. Hence chest x-ray and abdominal ultrasound can be useful tools for diagnosis. The degree of increase above the baseline hematocrit often reflects the severity of plasma leakage.
Shock occurs when a critical volume of plasma is lost through leakage. It is often preceded by warning signs. The body temperature may be subnormal when shock occurs. With prolonged shock, the consequent organ hypoperfusion (decreased blood flow to an organ) results in progressive organ impairment, metabolic acidosis and disseminated severe hemorrhage causing the hematocrit to decrease and the total white cell count may increase. In addition, severe organ impairment such as severe hepatitis (liver), encephalitis (brain) or myocarditis (heart) and/or severe bleeding may also develop without obvious plasma leakage or shock.
Those who improve after lowering of fever are said to have non-severe dengue. Some patients progress to the critical phase of plasma leakage who are still febrile and, in these patients changes in the full blood count should be used to guide the onset of the critical phase and plasma leakage. Those who deteriorate will manifest with warning signs.
Cases of dengue with warning signs will probably recover with early intravenous rehydration. Some cases will deteriorate to severe dengue.