title: Relative rates of non-pneumonic SARS coronavirus infection and SARS coronavirus pneumonia.
abstract: 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.
authors.affiliation: Department of Microbiology, University of Hong Kong, University Pathology Building, Queen Mary Hospital, Hong Kong.
authors.forename: Patrick C Y
authors.initials: PC
authors.lastname: Woo
authors.forename: Susanna K P
authors.initials: SK
authors.lastname: Lau
authors.forename: Hoi-wah
authors.initials: HW
authors.lastname: Tsoi
authors.forename: Kwok-hung
authors.initials: KH
authors.lastname: Chan
authors.forename: Beatrice H L
authors.initials: BH
authors.lastname: Wong
authors.forename: Xiao-yan
authors.initials: XY
authors.lastname: Che
authors.forename: Victoria K P
authors.initials: VK
authors.lastname: Tam
authors.forename: Sidney C F
authors.initials: SC
authors.lastname: Tam
authors.forename: Vincent C C
authors.initials: VC
authors.lastname: Cheng
authors.forename: Ivan F N
authors.initials: IF
authors.lastname: Hung
authors.forename: Samson S Y
authors.initials: SS
authors.lastname: Wong
authors.forename: Bo-jian
authors.initials: BJ
authors.lastname: Zheng
authors.forename: Yi
authors.initials: Y
authors.lastname: Guan
authors.forename: Kwok-yung
authors.initials: KY
authors.lastname: Yuen
mesh_terms: 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
chemical_list: 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