Relative rates of non-pneumonic SARS coronavirus infection and SARS coronavirus pneumonia.
BACKGROUND
Although the genome of severe acute respiratory syndrome coronavirus (SARS-CoV) has been sequenced and a possible animal reservoir identified, seroprevalence studies and mass screening for detection of subclinical and non-pneumonic infections are still lacking.


METHODS
We cloned and purified the nucleocapsid protein and spike polypeptide of SARS-CoV and examined their immunogenicity with serum from patients with SARS-CoV pneumonia. An ELISA based on recombinant nucleocapsid protein for IgG detection was tested with serum from 149 healthy blood donors who donated 3 years previously and with serum positive for antibodies against SARS-CoV (by indirect immunofluorescence assay) from 106 patients with SARS-CoV pneumonia. The seroprevalence of SARS-CoV was studied with the ELISA in healthy blood donors who donated during the SARS outbreak in Hong Kong, non-pneumonic hospital inpatients, and symptom-free health-care workers. All positive samples were confirmed by two separate western-blot assays (with recombinant nucleocapsid protein and recombinant spike polypeptide).


RESULTS
Western-blot analysis showed that the nucleocapsid protein and spike polypeptide of SARS-CoV are highly immunogenic. The specificity of the IgG antibody test (ELISA with positive samples confirmed by the two western-blot assays) was 100%, and the sensitivity was 94.3%. Three of 400 healthy blood donors who donated during the SARS outbreak and one of 131 non-pneumonic paediatric inpatients were positive for IgG antibodies, confirmed by the two western-blot assays (total, 0.48% of our study population).


CONCLUSIONS
Our findings support the existence of subclinical or non-pneumonic SARS-CoV infections. Such infections are more common than SARS-CoV pneumonia in our locality.
Woo
Patrick C Y
PC
Department of Microbiology, University of Hong Kong, University Pathology Building, Queen Mary Hospital, Hong Kong.
Lau
Susanna K P
SK
Tsoi
Hoi-wah
HW
Chan
Kwok-hung
KH
Wong
Beatrice H L
BH
Che
Xiao-yan
XY
Tam
Victoria K P
VK
Tam
Sidney C F
SC
Cheng
Vincent C C
VC
Hung
Ivan F N
IF
Wong
Samson S Y
SS
Zheng
Bo-jian
BJ
Guan
Yi
Y
Yuen
Kwok-yung
KY
D001782:Blood Donors; D015153:Blotting, Western; D002681:China / Q000453:epidemiology; D017934:Coronavirus / Q000235:genetics / Q000302:isolation & purification*; D003428:Cross Infection / Q000453:epidemiology / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis / Q000276:immunology; D008562:Membrane Glycoproteins / Q000032:analysis; D019590:Nucleocapsid Proteins / Q000235:genetics / Q000276:immunology; D011024:Pneumonia, Viral / Q000453:epidemiology* / Q000276:immunology / Q000821:virology; D011994:Recombinant Proteins / Q000032:analysis / Q000276:immunology; D016036:Seroepidemiologic Studies; D045169:Severe Acute Respiratory Syndrome / Q000453:epidemiology* / Q000276:immunology / Q000821:virology; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins / Q000032:analysis
D007074:Immunoglobulin G; D008562:Membrane Glycoproteins; D019590:Nucleocapsid Proteins; D011994:Recombinant Proteins; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV