SARS Antibody Test for Serosurveillance
SARS Antibody Test for Serosurveillance
A peptide-based enzyme-linked immunosorbent assay (ELISA) can be used for retrospective serosurveillance of severe acute respiratory syndrome (SARS) by helping identify undetected chains of disease transmission. The assay was developed by epitope mapping, using synthetic peptides from the spike, membrane, and nucleocapsid protein sequences of SARS-associated coronavirus. The new peptide ELISA consistently detected seroconversion by week 2 of onset of fever, and seropositivity remained through day 100. Specificity was 100% on normal blood donor samples, on serum samples associated with infection by other pathogens, and on an interference panel. The peptide-based test has advantages of safety, standardization, and automation over previous immunoassays for SARS. The assay was used for a retrospective survey of healthy healthcare workers in Taiwan who treated SARS patients. Asymptomatic seroconversions were detected in two hospitals that had nosocomial disease.
Retrospective surveillance for infection is an important means to screen for and interrupt undetected chains of disease transmission. Such surveillance may be key to tracking the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) because mild and asymptomatic cases of SARS-CoV infection that do not meet the World Health Organization's case definition have been identified by immunoassays, and SARS-CoV-like viruses have been isolated from wild mammals. SARS-CoV may have persisted over the summer in previously affected areas in such difficult-to-recognize reservoirs. The reemergence of SARS in the city of Guangzhou of the Guangdong Province of China in December 2003 and January 2004 is evidence that an unknown reservoir exists and signals the need for continued surveillance with laboratory testing.
The current laboratory methods for identifying SARS are not ideal tools for use in retrospective mass screening. Reverse transcription-polymerase chain reaction (RT-PCR) for detecting viral RNA is the most sensitive method for early identification of SARS. However, viral load rapidly declines beginning 9 or 10 days after disease onset. Moreover, RT-PCR requires sophisticated equipment and high laboratory quality-assurance standards. Identifying seroconversion to SARS-CoV by immunoassay also is a definitive criterion for laboratory determination of SARS, and seroconversion is the preferred standard for retrospectively detecting SARS-CoV infection. SARS immunoassays include the enzyme-linked immunosorbent assay (ELISA) or Western blot with antigen from whole virus or various recombinant proteins, a cumbersome immunofluorescence assay (IFA) using whole virus fixed on glass, and methods to determine neutralizing antibodies. Immunoglobulin (Ig) G to SARS-CoV, detected by these immunoassays, begins to rise sharply by day 11 after onset of symptoms. Virtually all SARS patients show virus-specific antibody by week 3, and anti-SARS-CoV IgG persists through day 100. Although any of these immunoassays can provide a definitive laboratory finding, all but the recombinant tests require biosafety level 3 to contain the virus or are time-consuming to perform, have not been well-standardized, are of unknown specificities, and would be difficult to adapt to large-scale manufacture. Improving laboratory methods for the large-scale serologic surveillance of SARS, particularly in the presence of other respiratory illnesses, and standardization of diagnostic assays are key priorities for controlling SARS. In this report, a standardized and rapid peptide-based SARS ELISA is characterized for sensitivity and specificity.
Beginning in April 2003, delay in recognizing SARS cases and in implementing isolation procedures led to several nosocomial clusters of SARS-CoV transmission in healthcare facilities in Taiwan. The results from a retrospective serologic survey by the peptide ELISA of healthcare workers from facilities affected by nosocomial outbreaks are presented as a working example.
A peptide-based enzyme-linked immunosorbent assay (ELISA) can be used for retrospective serosurveillance of severe acute respiratory syndrome (SARS) by helping identify undetected chains of disease transmission. The assay was developed by epitope mapping, using synthetic peptides from the spike, membrane, and nucleocapsid protein sequences of SARS-associated coronavirus. The new peptide ELISA consistently detected seroconversion by week 2 of onset of fever, and seropositivity remained through day 100. Specificity was 100% on normal blood donor samples, on serum samples associated with infection by other pathogens, and on an interference panel. The peptide-based test has advantages of safety, standardization, and automation over previous immunoassays for SARS. The assay was used for a retrospective survey of healthy healthcare workers in Taiwan who treated SARS patients. Asymptomatic seroconversions were detected in two hospitals that had nosocomial disease.
Retrospective surveillance for infection is an important means to screen for and interrupt undetected chains of disease transmission. Such surveillance may be key to tracking the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) because mild and asymptomatic cases of SARS-CoV infection that do not meet the World Health Organization's case definition have been identified by immunoassays, and SARS-CoV-like viruses have been isolated from wild mammals. SARS-CoV may have persisted over the summer in previously affected areas in such difficult-to-recognize reservoirs. The reemergence of SARS in the city of Guangzhou of the Guangdong Province of China in December 2003 and January 2004 is evidence that an unknown reservoir exists and signals the need for continued surveillance with laboratory testing.
The current laboratory methods for identifying SARS are not ideal tools for use in retrospective mass screening. Reverse transcription-polymerase chain reaction (RT-PCR) for detecting viral RNA is the most sensitive method for early identification of SARS. However, viral load rapidly declines beginning 9 or 10 days after disease onset. Moreover, RT-PCR requires sophisticated equipment and high laboratory quality-assurance standards. Identifying seroconversion to SARS-CoV by immunoassay also is a definitive criterion for laboratory determination of SARS, and seroconversion is the preferred standard for retrospectively detecting SARS-CoV infection. SARS immunoassays include the enzyme-linked immunosorbent assay (ELISA) or Western blot with antigen from whole virus or various recombinant proteins, a cumbersome immunofluorescence assay (IFA) using whole virus fixed on glass, and methods to determine neutralizing antibodies. Immunoglobulin (Ig) G to SARS-CoV, detected by these immunoassays, begins to rise sharply by day 11 after onset of symptoms. Virtually all SARS patients show virus-specific antibody by week 3, and anti-SARS-CoV IgG persists through day 100. Although any of these immunoassays can provide a definitive laboratory finding, all but the recombinant tests require biosafety level 3 to contain the virus or are time-consuming to perform, have not been well-standardized, are of unknown specificities, and would be difficult to adapt to large-scale manufacture. Improving laboratory methods for the large-scale serologic surveillance of SARS, particularly in the presence of other respiratory illnesses, and standardization of diagnostic assays are key priorities for controlling SARS. In this report, a standardized and rapid peptide-based SARS ELISA is characterized for sensitivity and specificity.
Beginning in April 2003, delay in recognizing SARS cases and in implementing isolation procedures led to several nosocomial clusters of SARS-CoV transmission in healthcare facilities in Taiwan. The results from a retrospective serologic survey by the peptide ELISA of healthcare workers from facilities affected by nosocomial outbreaks are presented as a working example.
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