Objective: To compare the sensitivity and specificity of four kits for detection of anti-severe acute respiratory syndrome (SARS)-CoV IgG in sera of SARS patients.
Methods: Anti-SARS-CoV IgG was detected in 99 serial sera from 18 SARS patients and in 123 negative reference sera, using two enzyme linked immunosorbent assays (EIA No. A and No. B) and two indirect immunofluorescence assays (Australian IFA and Euroimmun IFA).
Results: Anti-SARS-CoV IgG was not detected in sera collected from SARS patients at the first week after onset by any of the four kits, however, it was detectable in sera obtained at the second week of illness by EIA No. B, and two IFA, but not by EIA No. A, with the positive rates of 57.1% (4/7), 57.1% (4/7) and 42.9% (3/7), respectively. The anti-SARS-CoV IgG was first determined in sera on the 9th day by Euroimmun IFA, 12th day by EIA No. B, 13th day by Australian IFA, and 16th day by EIA No. A. The positive rates of antibody on the 3rd week after onset were 84.2% (16/19), 94.7% (18/19), 78.9% (15/19) and 52.6% (10/19) respectively. They were identical since the 4th week after the disease onset. Through detection of 123 negative reference sera, the specificity of EIA No. A and two IFA was 100%, with exception of 94.9% for EIA No. B.
Conclusion: The sensitivity and specificity of the two IFAs were relatively higher than that of the two EIAs. The quality of the two homemade EIAs should be improved.