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Dengue

Dengue

Causative Agent

Dengue virus types 1 to 4

Incubation Period

5 – 7 days (range 3 – 14 days)

Infectious Period

From up to 2 days before illness onset to 5 days after illness onset.

Transmission

Transmitted by Aedes aegypti and Aedes albopictus mosquitoes.

Epidemiology

A total of 4497 cases of DF/DHF were reported in 2009 compared to 7031 cases in 2008. Of the reported cases, 46 (1.0%) cases were notified as DHF. The incidence rate among local residents was highest in the 15-24 year age group with a male to female ratio of 1.6:1.

Most infections in children are subclinical whereas infections in adults are more likely to be symptomatic. All four serotypes of dengue virus are present in Singapore. The disease is endemic in most countries in the tropics, Africa, the Caribbean, Central and South America as well as Southeast Asia.


Dengue fever

  • Fever: acute onset, lasts for 2 - 7 days plus
  • Two or more of the following:
    • Headache, backache, myalgia
    • Rash: maculopapular or flush; petechial with islands of sparing
    • Retro-orbital pain
    • Bleeding
    • Leucopenia
  • Thrombocytopenia may also occur and usually worsens at the time when fever resolves

Dengue haemorrhagic fever

Diagnostic criteria:

  • Fever plus
  • Bleeding manifestations (e.g. petechiae, ecchymosis, epistaxis, gum bleeding, haematemesis, melena) plus
  • Thrombocytopenia (< 100 X 109/L) plus
  • Evidence of increased capillary permeability:
    • haematocrit increased by >20% above baseline
    • pleural effusion
    • hypoalbuminaemia

Dengue shock syndrome

  • As above plus
  • Hypotension, narrowed pulse pressure (< 20 mm Hg) and impaired organ perfusion.

In 2009, WHO revised the dengue classification scheme in response to studies indicating that the 1997 scheme described above may underestimate severe disease in adults compared to children. Using this scheme, dengue illness can be classified clinically as follows:

Dengue

  • Fever plus
  • Two or more of the following:
    • Nausea, vomiting
    • Rash
    • Aches and pains
    • Tourniquet test positive
    • Leucopenia
  • Warning signs suggestive of severe dengue may or may not be present. These are:
    • Abdominal pain/tenderness
    • Persistent vomiting
    • Clinical fluid accumulation
    • Mucosal bleeding
    • Lethargy, restlessness
    • Liver enlargement > 2cm
    • Haematocrit increase concurrent with rapid decrease in platelet count

Severe dengue

Severe dengue illness can be one of the following:

  • Severe plasma leakage
    • Shock (dengue shock syndrome)
    • Fluid accumulation with respiratory distress
  • Severe bleeding
  • Severe organ impairment
    • Liver: AST or ALT > 1000 IU
    • CNS: impairment of consciousness
    • Heart or other organs

Differential diagnosis

A wide spectrum of viral, bacterial and parasitic infections mimic DF/DHF in the febrile phase. Chikungunya fever is very similar to DF and mild DHF. Marked thrombocytopenia with concurrent haemoconcentration differentiates DHF from diseases such as endotoxin shock from bacterial infection or meningococcaemia.


  • FBC: thrombocytopenia, leucopenia, raised haematocrit.
  • LFTs: mild to moderate elevated transaminases (usually AST > ALT).
  • Serology: Positive dengue IgM on acute serum sample. A high-titre IgG antibody may also be indicative of dengue, particularly secondary infection. IgM antibodies appear on approximately the fifth day of illness and last for two months. A 4-fold rise in titres of a pair of acute and convalescent sera is confirmatory.
  • PCR for dengue virus within five days of onset may give a more rapid diagnosis.


A legally notifiable disease in Singapore. Notify Ministry of Health (Form MD 131 or electronically via CD-LENS) not later than 24 hours from the time of diagnosis.

The residential address and place of work/school should be given.

DHF cases should be re-notified if they are initially notified as DF and subsequently fulfil criteria for DHF (see above).



  • Supportive.
  • Paracetamol for fever (avoid non-steroidal anti-inflammatory drugs).
  • Intravenous fluids for hypotension and dehydration (avoid over-hydration precipitating pulmonary oedema in DHF).
  • Daily platelet and haematocrit measurement when platelets drop below 100,000/mm3.
  • Complete bed rest for platelet count less than 50,000/mm3.
  • There is no evidence that prophylactic platelet transfusion (in the absence of bleeding) is beneficial.


The National Environment Agency carries out entomological investigation around the residence and/or workplace of notified cases, particularly if these cases form a cluster where they are within 200 meters of each other. They also carry out epidemic vector control measures in outbreak areas and areas of high Aedes population identified on routine surveillance; and intensive public education to remove Aedes breeding habitats.











References

  1. Dengue: Guidelines for diagnosis, treatment, prevention and control. Geneva, WHO 2009.
  2. Ooi EE, Goh KT, Gubler DJ. Dengue prevention and 35 years of vector control in Singapore.  Emerg Infect Dis 2006; 12:887-93
  3. Koh BKW, Ng LC, Kita Y et al. The 2005 dengue epidemic in Singapore: epidemiology, prevention and control. Ann Aca Med Singapore 2008;37:538-45.
  4. Yew YW, Ye T, Ang LW et al. Seroepidemiology of dengue virus infection among adults in Singapore. Ann Acad Med Singapore 2009;38:667-75.






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