Dengue can be diagnosed by isolation of the virus, by serological tests, or by molecular methods. Diagnosis of acute (on-going) or recent dengue infection can be established by testing serum samples during the first 5 days of symptoms and/or early convalescent phase (more than 5 days of symptoms). Acute infection with dengue virus is confirmed when the virus is isolated from serum or autopsy tissue specimens, or the specific dengue virus genome is identified by reverse transcription-polymerase chain reaction (RT–PCR) from serum or plasma, cerebrospinal fluid, or autopsy tissue specimens during an acute febrile illness. Methods such as one-step, real time RT–PCR or nested RT–PCR are now widely used to detect dengue viral genes in acute-phase serum samples. This detection coincides with the viremia and the febrile phase of illness onset. Acute infections can also be laboratory confirmed by identification of dengue viral antigen or RNA in autopsy tissue specimens by immunofluorescence or immunohistochemical analysis, or by seroconversion from negative to positive IgM antibody to dengue or demonstration of a fourfold or greater increase in IgG antibody titers in paired (acute and convalescent) serum specimens. Patients who have IgM antibodies to dengue detected in their serum specimen via an IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA) and had either 1.) A negative RT–PCR result in the acute phase specimen or 2.) Did not submit an acute phase specimen, are classified as having arecent probable dengue infection. This is due to the fact that IgM antibodies for dengue may remain elevated for 2 to 3 months after the illness. The elevated IgM observed in a sample could be the result of an infection that occurred 2 to 3 months ago. In addition, there is cross reactivity with other flaviviruses including West Nile virus (WNV), St. Louis encephalitis virus (SLE), Japanese encephalitis virus (JEV) and yellow fever virus (YFV). The provider should review the patient’s past medical history, recent travel history, and vaccination record (especially yellow fever vaccination) to determine the likelihood that the current acute febrile illness is due to an infection with dengue virus. Often times both an acute and convalescent phase specimens are needed to make a diagnosis of dengue infection. This is especially true for those who submit a day 5 acute specimen because the virus and IgM antibodies may be at undetectable levels. So if a patient with suspected dengue infection submits a late acute phase specimen that is negative (e.g., by RT–PCR and MAC-ELISA), and they do not submit a convalescent specimen, they are classified as a laboratory-indeterminate case.
Posted on: Tue, 10 Sep 2013 08:07:53 +0000
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