Rapid diagnosis of hantavirus disease with an IgG-avidity assay

Nephropathia epidemica (NE), due to Puumala virus, is endemic in eastern Europe and Scandinavia. Serodiagnosis of NE relies on conventional indirect immunofluorescence to detect IgG against Puumala virus. However, in conventional serology, most patients with acute NE have raised but stable non-diagnostic antibody titres. For better serodiagnosis of NE, we have developed a test that measures the avidity (functional affinity) of IgG antibodies against Puumala virus. This new assay was highly specific and sensitive; a diagnosis of NE could be confirmed or excluded rapidly from an early single serum sample. With this test we have now verified the diagnosis of NE in more than 1300 Finnish patients during 22 months in 1989-91. Our findings point to an incidence of confirmed hantavirus disease much higher than previously shown.