Analysis of false-positive associated with antibody tests for SARS-CoV in MCTD、SS and RA patients

To investigate the specificity of serological diagnostic testing for coronavirus antibody in patients with severe acute respiratory syndrome(SARS) and to discuss the fasle-positive of SARS-associated coronavirus(SARS-CoV) antibody in patients with Sjogren's syndrome(SS),rheumatoid arthritis(RA) and mixed connective tissue disease(MCTD) . SARS-CoV IgG and IgM antibody was detected in serum specimens from 46 SS、MCTD and RA patients with non-SARS and 111 healthy controls without SARS-CoV infection by enzyme-linked immunosorbent assays(ELISA) and indirect immunofluorescence antibody(IFA). The results showed that SARS-CoV antibody positive rates of SS、MCTD and RA patients and healthy controls were 19.6% (9/46) and 3.6%(4/111) respectively. Of all samples with positive SARS-CoV antibody for SS、MCTD and RA patients using ELISA were all negative by IFA. This results suggests that the specificity of IFA tests for SARS is 100%, but there are few false-positive rates of SARS-CoV antibody in samples without SARS-CoV infection by ELISA.