Dengue Classification
Dengue is classified using the revised WHO 2009 system into three categories based on clinical severity: Dengue without Warning Signs, Dengue with Warning Signs, and Severe Dengue—this classification system demonstrates superior sensitivity (92.1%) and specificity (78.5%) for identifying patients requiring intensive care compared to the traditional classification. 1, 2
Revised WHO Classification System (2009)
The current standard categorizes dengue into three distinct groups 1:
1. Dengue without Warning Signs
- Acute febrile illness with frontal headache, retro-orbital pain, muscle and joint pain, and rash 3
- Patients can be safely managed on an outpatient basis 4
- Represents approximately 31% of confirmed dengue cases 5
2. Dengue with Warning Signs
This category requires close monitoring and consideration for hospitalization 1, 6. Warning signs include 6:
- Persistent vomiting
- Abdominal pain or tenderness
- Clinical fluid accumulation
- Mucosal bleeding
- Lethargy or restlessness
- Hepatomegaly (liver enlargement)
- Hematocrit rise with concurrent thrombocytopenia
Warning signs typically appear around day 3-7 of illness, coinciding with defervescence (when fever subsides) 1, 6. This category represents approximately 58.4% of confirmed cases 5.
3. Severe Dengue
Severe Dengue is defined by the presence of any of the following 1, 2:
- Severe plasma leakage leading to shock or fluid accumulation with respiratory distress
- Severe bleeding
- Organ failure (liver AST/ALT >1000, impaired consciousness, heart or other organ involvement)
This classification captures 92.1% of patients requiring intensive care 2 and represents approximately 10.6% of confirmed cases 5.
Traditional WHO Classification (1997)
The older system classified dengue as 3:
Dengue Fever (DF)
- Acute febrile illness with characteristic symptoms
Dengue Hemorrhagic Fever (DHF)
- Acute febrile illness with minor or major bleeding phenomena
- Thrombocytopenia ≤100,000/mm³ 3
- Evidence of plasma leakage documented by hemoconcentration (hematocrit increased ≥20%) or other objective evidence of increased capillary permeability 3
- Graded I-IV based on severity 5
Dengue Shock Syndrome (DSS)
- All DHF criteria plus hypotension or narrow pulse pressure ≤20 mm Hg 3
The traditional classification has lower sensitivity (39.0%) for identifying patients requiring intensive care, making it less clinically useful 2.
Key Diagnostic Considerations
Daily monitoring of complete blood count is essential to track platelet counts and hematocrit levels 1. Laboratory confirmation should utilize 1, 6:
- PCR testing: Most effective in the first few days during viremia 6
- NS1 antigen detection: Useful from day 1 to day 10 after symptom onset 6
- IgM antibody testing: Appropriate after the first week of illness 6
Critical Clinical Pitfalls
Age is the key variable for risk stratification, with children requiring closer monitoring of warning signs 7. Ultrasonography is the most sensitive technique (100% detection) for identifying plasma leakage, compared to hemoconcentration (44.7%) or chest x-ray (86.3%) 5.
Vomiting and abdominal pain are common warning signs but also occur in non-dengue febrile illnesses, requiring dengue confirmatory testing for proper classification 5. The revised classification may misclassify non-dengue patients with gastrointestinal bleeding as Severe Dengue 5.
Early recognition of warning signs and appropriate management can reduce case-fatality rate to <0.5% 6.