title: The clinical usefulness of a Puumalavirus recombinant nucleocapsid protein based enzyme-linked immunosorbent assay in the diagnosis of nephropathia epidemica as compared with an immunofluorescence assay.
abstract: BACKGROUND
  Nephropathia epidemica (NE), a hemorrhagic fever with renal syndrome (HFRS) predominantly encountered in northern Europe, is a febrile disease, commonly associated with acute renal impairment. A rapid and reliable serological diagnosis is required to differentiate NE from other acute febrile illnesses in endemic areas.
  
  
  OBJECTIVE
  To evaluate a Puumala (PUU) virus recombinant nucleocapsid protein (rN) based enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of NE as compared with an immunofluorescence assay (IFA) in a clinically relevant patient sample.
  
  
  METHODS
  During a four-month period, 618 serum samples from 512 patients with an illness suggestive of NE, sent to the Department of Clinical Virology for serological analysis, were included in the study. All sera were tested by PUU rN ELISA for presence of specific IgG, IgM and IgA antibodies and by IFA using PUU virus infected cells as antigen for presence of IgG and IgM antibodies. Patients with discordant results by IFA and rN ELISA were further serologically and/or clinically evaluated to assess the probability of NE.
  
  
  RESULTS
  Compared to IFA, the specificities of the IgM and IgG rN ELISA were 100% and the corresponding sensitivities were 94.0%. The positive and negative predictive values of the PUU IgM rN ELISA in diagnosing NE infection was 100 and 98.6%, respectively. The positive predictive values for present NE infection of IgG rN ELISA and IFA were 68.3 and 71.4%, respectively. The positive predictive value of IgA rN ELISA was 95.8% and the negative 92.7%.
  
  
  CONCLUSIONS
  The demonstration of specific IgM by rN ELISA is a highly specific and reliable method for the serological confirmation of NE. Detection of IgG antibodies by rN ELISA or IFA has a low predictive value to diagnose NE in an endemic area. The diagnostic value of IgA determination is in between IgM and IgG determinations.
authors.affiliation: Department of Virology, University of Umeå, S-901 85 Umeå, Sweden. Fredrik.Elgh@clmi.umu.se
authors.forename: F
authors.initials: F
authors.lastname: Elgh
authors.forename: M
authors.initials: M
authors.lastname: Linderholm
authors.forename: G
authors.initials: G
authors.lastname: Wadell
authors.forename: P
authors.initials: P
authors.lastname: Juto