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Dengue is a viral infection transmitted by the bite of an infected mosquito. There are four closely related but antigenically different serotypes of the virus that can cause dengue (DEN1, DEN2, DEN3 and DEN4). Dengue has a wide spectrum of infection outcomes (asymptomatic to symptomatic). Symptomatic illness can vary from undifferentiated fever (viral syndrome), dengue fever (DF), dengue haemorrhagic fever (DHF) and dengue with unusual manifestations. DF and DHF comprise the bulk of symptomatic illness while unusual dengue is a rare entity (usually <1%).

Dengue Fever (DF) – marked by an onset of sudden high fever, severe headache, pain behind the eyes, and pain in muscles and joints. Some may also have a rash and varying degree of bleeding from various parts of the body (including nose, mouth and gums or skin bruising).

Dengue Haemorrhagic Fever (DHF) – is a more severe form, seen only in a small proportion of those infected. DHF is a stereotypic illness characterized by 3 phases; febrile phase with high continuous fever usually lasting for less than 7 days; critical phase (plasma leaking) lasting 1-2 days usually apparent when fever comes down, leading to shock if not detected and treated early; convalescence phase lasting 2-5 days with improvement of appetite, bradycardia (slow heart rate), convalescent rash (white patches in red background), often accompanied by generalized itching (more intense in palms and soles), and diuresis (increase urine output).

Patients should seek medical advice in the presence of following features particularly when fever settles:

  • Severe vomiting
  • Abdominal pain  
  • Increase thrust
  • Drowsiness and excessive sleepiness
  • Refusing to eat or drink
  • Abnormal bleeding manifestations – eg: heavy menstrual bleeding or menstruation starting earlier than usual
  • Reduced urine output

If the following features are present seek medical attention immediately:

  • Cold clammy skin and extremities
  • Restless and irritability
  • Skin mottling
  • Decreased/no urine output
  • Behaviour changes – confusion or using foul language

Early detection of Dengue illness

Early identification and management of Dengue illness can minimize morbidity and mortality. In the present hyper-endemic setting in Sri Lanka, Dengue illness (Dengue Fever - DF /Dengue Haemorrhagic Fever - DHF) is considered in the differential diagnosis of patients presenting   with acute onset of fever with headache, retro-orbital pain, myalgia, arthralgia, rash (diffuse, erythematous, macular), haemorrhagic manifestation (petechiae, positive tourniquet test), Leukopenia (<5000/mm3), Platelet count ≤150,000/mm3 and rising Haematocrit of 5-10%.

Sometimes Dengue patients may present with atypical manifestations like respiratory symptoms such as cough, rhinitis or injected pharynx and gastro-intestinal symptoms such as constipation, colicky abdominal pain, diarrhoea or vomiting without the classical clinical presentation described above.

If a patient with high fever is seen with flushed face/extremities (diffuse blanching erythema in adults) and a positive tourniquet test (even with a normal platelet count) with leukopenia (WBC <5000 /mm3) without a focus of infection, it is very likely that the patient is having Dengue illness.

In any patient who presents with shock (particularly afebrile at presentation with cold extremities and tachycardia with low volume pulse and hypotension) consider Dengue Shock as a likely diagnosis. 

Detection of NS1 antigen from blood is novel laboratory diagnostic test for dengue during early febrile phase. However, NS1 only implies that the person is having dengue illness and it does not help in differentiating DF from DHF. Therefore, NS1 test may be useful in situations where early clinical diagnosis is doubtful.

Value of Full Blood Count (FBC/CBC)

OPD level:
  • FBC is mandatory on all fever patients – from day 3 onwards
  • Special patient categories – FBC on day 1 or first day of visit/contact (Pregnancy, Infancy, elderly, those with co-morbidities, etc.)
  • FBC daily from day 3 if platelet (plt) count ≥150,000/ mm3
  • FBC twice daily when plt count  ≤150,000/ mm3  (admission to hospital based on clinical judgment, warning signs and social reasons)
  • Admit/ refer all patients with platelet count ≤130,000/ mm3
Inward level:
  • For any patient admitted to hospital on or before day 3 of illness same criteria of performing FBC as in OPD level is applicable unless and otherwise more frequent counts are requested by the clinician.

Important Advice for Ambulatory Care Patients (At home care):

  • First contact doctors should ensure adequate oral fluid intake.
  • Drink enough fluids to maintain a normal urine output. Follow the instructions below to calculate the required fluid amount.
  • If the body weight is between 30 to 50 kilograms, take fluids double the weight in milliliters per hour.
  • If the weight is below 30 kilograms or above 50 kilograms change the fluid intake as shown below

Body WeightFluid Volume per hour
  • If there is any doubt about how much fluids to drink please ask your doctor.
  • You may use a properly calibrated cup to measure the fluid intake.
Urine Output
  • Ensure adequate amount of fluids are taken to produce a urine volume per hour in milliliters (ml) equal to your body weight in kilograms to prevent dehydration.
  • Ensure urine measurement at least every four hourly to calculate the output.

Body WeightUrine Output per hourUrine Output per four hours
  • Passing urine slightly more than the expected amount is not a problem.
  • If the urine output is less than the expected amount, you should consume more fluids to maintain the above urine output.
  • If the patient is feeling thirsty, taking additional fluids up to 3-4 times per day is allowed until the thirst subsides.
  • But if the thirst continues, consult your doctor as soon as possible.

Patients/parents should be asked to return immediately for review if any of the following occur on/beyond day three:

  • Clinical deterioration with settling of fever
  • Inability to tolerate oral fluid
  • Severe abdominal pain
  • Cold and clammy extremities
  • Lethargy or irritability/restlessness
  • Bleeding tendency including inter-menstrual bleeding or menorrhagia
  • Not passing urine for more than 6 hours

Differentiation of DHF from DF:

It is important to differentiate DHF from DF early because it is the patients with DHF who develop plasma leakage and resultant complications usually after the third day of fever. DHF may become evident as the fever settles. Tachycardia (increase heart rate) without fever (or disproportionate tachycardia with fever) and narrowing of pulse pressure (eg: difference between systolic and diastolic narrows from 40mmHg to 30 mmHg) is an early indication of leaking which warrants referral to the hospital. A progressively rising Haematocrit suggests that the patient may have entered the leaking phase. However, an ultra sound scan focused on chest and abdomen to detect selective and progressive fluid accumulation is a more objective evidence of plasma leakage in DHF. 

Admission to a hospital:

The first contact doctor will decide to admit a patient to a hospital based on the clinical judgment. It is essential to admit the following patients:

  • Platelet count below<130,000/mm3 or if there is a rapid reduction in the platelet count.
  • With the following warning signs on or beyond day 3 of fever/illness:
    • Abdominal pain or tenderness
    • Persistent vomiting
    • Mucosal bleeding (eg: bleeding from mouth, nose etc.)
    • Lethargy, restlessness
    • Liver enlargement >2cm
    • Rising HCT with rapid decrease in platelet count in FBC
    • Clinical signs of plasma leakage: pleural effusion, ascites (late sign)

Other patients who may need admission even without above criteria are:

  • Pregnant mothers - admission on second day of fever and close follow up with daily FBC is very important.
  • Elderly patients/infants
  • Obese patients
  • Patients with co-morbid conditions like diabetes, chronic renal failure, ischemic heart disease, haemoglobinopathies such as thalassaemia and other major medical problems
  • Patients with adverse social circumstances -e.g. living alone, living far from health facility without reliable means of transport.

Clinical (improved well-being and appetite with normal urine output) and haemo-dynamical stability with no fever for 48 hours indicates recovery from Dengue illness.