Case definition for dengue fever

00000000Given the variability in the clinical illness associated with dengue infection, it is not appropriate to adopt a detailed clinical definition of dengue fever. Rather, the need for laboratory confirmations emphasized.
The following classifications are proposed:

• Probable-an acute febrile illness with two or more of the following manifestations:
  -- headache
  -- retro-orbital pain
  -- myalgia
  -- arthralgia
  -- rash
  -- haemorrhagic manifestations
  -- leukopenia;
  and
  -- supportive serology (a reciprocal haemagglutination-inhibition antibody titre > 1280, a comparable IgG enzyme-linked immunosorbent assay (ELISA, see Chapter 4) titre or a positive IgM antibody test on a late acute or convalescent-phase serum specimen);
  or
  -- occurrence at the same location and time as other confirmed cases of dengue fever.
  
• Confirmed-a case confirmed by laboratory criteria (see below).
  
• Reportable-any probably or confirmed case should be reported.
  Laboratory criteria for confirmation of dengue fever are (see Chapter 4):
  
• Isolation of the dengue virus from serum or autopsy samples; or
  
• Demonstration of a fourfold or greater change in reciprocal IgG or IgM antibody titres to one or more dengue virus antigens in paired serum samples; or
  
• Demonstration of dengue virus antigen in autopsy tissue, serum or cerebrospinal fluid samples by immunohistochemistry, immunofluorescence or ELISA; or
  
• Detection of dengue virus genomic sequences in autopsy tissue serum or cerebrospinal fluid samples by polymerase chain reaction (PCR).
  

Case definition for dengue haemorrhagic fever
The following must all be present:

• Fever, or history of acute fever, lasting 2 - 7 days, occasionally biphasic.
  
• Haemorrhagic tendencies, evidenced by at least one of the following:
  -- a positive tourniquet test1
  -- petechiae, ecchymoses or purpura
  -- bleeding from the mucosa, gastrointestinal tract, injection sites or other locations
  -- haematemesis or melena.
  
• Thrombocytopenia (100 000 cells per mm3 or less).2
  
• Evidence of plasma leakage due to increased vascular permeability, manifested by at least one of the following:
  -- a rise in the haematocrit equal to or greater than 20% above average for age, sex and population;
  -- a drop in the haematocrit following volume-replacement treatment equal to or greater than 20% of baseline;
  -- signs of plasma leakage such as pleural effusion, ascites and hypoproteinaemia.
  
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  1 The tourniquet test is performed by inflating a blood pressure cuff on the upper arm to a point midway between the systolic and diastolic pressures for 5 minutes. A test is considered positive when 20 or more petechiae per 2.5 cm (1 inch) square are observed. The test may be negative or mildly positive during the phase of profound shock. It usually becomes positive, sometimes strongly positive, if the test is conducted after recovery from shock.
  2 This number represents a direct count using a phase-contrast microscope (normal is 200 000 - 500 000 per mm3). In practice, for outpatients, an approximate count from a peripheral blood smear is acceptable. In normal persons, 4 - 10 platelets per oil-immersion field (100x; the average of the readings from 10 oil-immersion fields is recommended) indicates an adequate platelet count. An average of < 3 platelets per oil-immersion field is considered low (i.e. < 100 000 per mm3).