Detection of anti-SARS CoV IgG antibody in sera of different populations and its significance

Objective To evaluate the significance of the anti-SARS CoV IgG in sera of different populations, using enzyme linked immunosorbent assay (EIA). Methods EIA, indirect fluorescence assays (IFA) and Western blot (WB) were used for the detection of the anti-SARS CoV IgG in serum. Results Dynamics of the anti-SARS CoV IgG were studied in 336 serial sera from 117 clinically diagnosed SARS patients. The antibody was first detected on the 9 th day after onset of the disease. The positive rates of the anti-SARS CoV IgG increased with the course of the illness, i.e. 12.5%(1/8), 73.9%(17/23), 91.5%(43/47), 96.6%(57/59) and 100%(198/198) respectively, on 5-9, 10-14, 15-19, 20-24 and 25 days after onset. Of 1?223 non-SARS individuals including 367 healthy workers working in SARS wards for more than 1 month, 43 close contacts with clinically diagnosed SARS patients and 813 persons without exposure to SARS CoV,28 were anti-SARS CoV IgG weak positive with the A value less than 0.5 by EIA screening. The antibody was negative in these 28 sera when re-tested by IFA and/or WB, indicating false positivity by EIA. Conclusion The detection of anti-SARS CoV IgG by EIA is useful for diagnosis of SARS patients at the middle and late phases of the disease. The specimens with weak positivity ( A value less than 0.5)of anti-SARS CoV IgG screened by EIA should be retested using IFA and/or WB to rule out the false reactivity.