Dengue Fever: Case Definition & Classification

Detailed analysis on Dengue Fever: Case Definition & Classification. Dengue fever is a mosquito-borne tropical disease caused by the dengue virus. Moreover, Symptoms typically begin three to fourteen days after infection. Additionally, These may include a high fever, headache, vomiting, muscle and joint pains, and a characteristic skin rash.

Recovery takes a week. In a small proportion of cases, the disease develops into the life-threatening dengue hemorrhagic fever, resulting in bleeding, low levels of blood platelets and blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs.

Clinical Description

According to the WHO, Dengue is defined by FEVER as reported by the patient or healthcare provider and the presence of one or more of the following signs and symptoms:

  • Nausea/vomiting
  • Rash
  • Aches and pains (e.g., headache, retro-orbital pain, joint pain, myalgia, arthralgia)
  • Tourniquet tests positive
  • Leukopenia (a total white blood cell count of <5,000/mm3), or
  • Any warning sign for severe dengue:
    • Abdominal pain or tenderness
    • Persistent vomiting
    • Extravascular fluid accumulation (e.g., pleural or pericardial effusion, ascites)
    • Mucosal bleeding at any site
    • Liver enlargement >2 centimetres
    • Increasing hematocrit concurrent with rapid decrease in platelet count

Classification of Dengue

Dengue has a wide spectrum of clinical presentations, often with unpredictable clinical evolution and outcome. While most patients recover following a self-limiting non-severe clinical course, a small proportion progress to severe disease, mostly characterized by plasma leakage with or without hemorrhage.

Moreover, Intravenous rehydration is the therapy of choice; this intervention can reduce the case fatality rate to less than 1% of severe cases. Additionally, The group progressing from non-severe to severe disease is difficult to define, but this is an important concern since appropriate treatment may prevent these patients from developing more severe clinical conditions.

Moreover, The case classification influences Triage, appropriate treatment, and the decision as to where this treatment should be given (in a health care facility or at home) for dengue. This is, even more, the case during the frequent dengue outbreaks worldwide, where health services need to be adapted to cope with the sudden surge in demand.

However, Changes in the epidemiology of dengue, as described in the previous sections, lead to problems with the use of the existing WHO classification.

Symptomatic dengue virus infections can be grouped into three categories:

  • Undifferentiated Fever
  • Dengue Fever (DF)
  • Dengue Hemorrhagic Fever (DHF).

Additionally, DHF is classified into four severity grades, with grades III and IV are defined as dengue shock syndrome (DSS). However, there have been many reports of difficulties in the use of this classification, which are summarized in a systematic literature review.

Moreover, Difficulties in applying the criteria for DHF in the clinical situation, together with the increase in clinically severe dengue cases which did not fulfill the strict criteria of DHF, led to the request for the classification to be reconsidered.

Currently, the classification into DF/DHF/DSS continues to be widely used and is show below:

 

Classification of dengue virus infection according to WHO

Expert consensus groups in Latin America (Havana, Cuba, 2007), South-East Asia (Kuala Lumpur, Malaysia, 2007), and at WHO headquarters in Geneva, Switzerland in 2008 agreed that:

“dengue is one disease entity with different clinical presentations and often with unpredictable clinical evolution and outcome.”

Additionally, the classification into levels of severity has a high potential for being of practical use. The user is in the clinicians’ decision as to where and how intensively the patient should is observed and treated,.

Moreover, the usage prevails in more consistent reporting in the national and international surveillance system, and as an end-point measure in dengue vaccine and drug trials.

However, A WHO-supported prospective clinical multicentre study across dengue-endemic regions was set up to collect evidence about criteria for classifying dengue into levels of severity.

Different Stereotypes of Dengue

Dengue Virus (DENV)-1, DENV-2, DENV-3, DENV-(4&5) each generating a unique host immune response to the infection. Additionally, Out of all first four stereotypes (DENV 1-4) are genetically similar and share approximately 65% of their genomes.

Moreover. Dengue virus is transmitted to non-human primates (sylvatic form) and humans (human form) via a mosquito vector; primarily of the genus Aedes.

Additionally, The fifth variant DENV-5 was isolated in October 2013. This serotype follows the sylvatic cycle, unlike the other four stereotypes which follow the human cycle.

Furthermore, The likely cause of the emergence of the new serotype could be genetic recombination, natural selection, and genetic bottlenecks. Although there is no indication of the presence of DENV-5 in India.

References:

  • The WHO dengue classification and case definitions: time for a reassessment. Lancet, 2006 & 2009
  • Severe dengue: the need for new case definitions. Lancet Infectious Diseases, 2006
  • Bandyopadhyay S, Lum LC, Kroeger A. Classifying dengue: a review of the difficulties in using the WHO case classification for dengue hemorrhagic fever.
  • WHO.” Dengue Fever classification “, 2nd ed. Geneva, World Health Organization, 1997.

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