Interpreting paired serology for Ross River virus and Barmah Forest virus diseases

Ross River virus (RRV) and Barmah Forest virus (BFV) cause approximately 4000 and 1000 cases, respectively, of rheumatic disease in Australia every year. Confirmation of a diagnosis usually involves testing for virus-specific immunoglobulin (Ig) M and IgG by a National Association of Testing Authorities-accredited pathology facility.

The aim of the article is to provide a logical framework by which clinicians can interpret paired RRV and BFV serology results in environments in which numerical antibody titres are no longer routinely provided. The traditional recommendation to look for an increase in titres is now largely obsolete.

Paired serology is clinical best practice but needs to be appropriately interpreted given the false positive and negative rates, the large number of asymptomatic infections and the long-term persistence of IgM in some individuals. An inappropriate interpretation risks a misdiagnosis.