Nucleocapsid protein as early diagnostic marker for SARS

Abstract

Serum samples from 317 patients with patients with severe acute respiratory syndrome (SARS) were tested for the nucleocapsid (N) protein of SARS-associated coronavirus, with sensitivities of 94% and 78% for the first 5 days and 6-10 days after onset, respectively. The specificity was 99.9%. N protein can be used as an early diagnostic maker for SARS.

Figure 1

N protein detection in 420 serum samples from 317 patients with severe acute respiratory syndrome (SARS). Data represent the optical density at 450 nm (OD₄₅₀) of undiluted serum samples. To establish the normal range of the N protein–capture enzyme-linked immunosorbent assay, serum specimens from 400 healthy blood donors were analyzed. The mean OD₄₅₀ for these specimens, as determined by the assay, was 0.078, with a standard deviation of 0.023. The cutoff OD₄₅₀ of the assay was then calculated as follows: cutoff = mean of OD₄₅₀ from 400 normal serum + 5 x standard deviations = 0.19. Solid line represents cutoff value. The result was considered positive if a sample yielded OD₄₅₀ above the cutoff.

Figure 2

The profile of N protein detection in blood and antibody response to severe acute respiratory syndrome-associated coronavirus (SARS-CoV) from onset of symptoms to the convalescent phase. IgG, immunoglobulin G.