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Suspected cases are confirmed by blood tests measuring two classes of antibodies, IgG and IgM.

Diagnosis can only be regarded as conclusive if a seroconversion to IgG (result goes from negative to positive) or four-fold rise in IgG antibody titre is detected in two blood samples taken at least two weeks apart, one at the beginning of illness and the second one 2-4 weeks later.

IgM antibody is a class of antibodies which are often used as indicators of recent infection. However, it is important to remember that in Barmah Forest virus disease this class of antibodies may be detected for long periods of time after the infection (18 to 48 months) and false-positive results with some test systems are not uncommon, particularly if you are infected with a different virus (cross-reaction). False-positive results have also been seen in individuals with autoimmune disease. When clinically important, it may be useful to have positive IgM antibody results verified by a reference laboratory. Testing for Barmah viral nucleic acid (RNA) can also be performed by reference laboratories but its use is limited to early in the disease course.

Diagnostic laboratories are required by law to report all positive cases to local public health units.

Last Review Date: August 1, 2018