title: Anti-SARS-CoV IgG response in relation to disease severity of severe acute respiratory syndrome.
abstract: BACKGROUND
  The association between a robust or depressed antibody response and clinical severity of SARS remains unknown.
  
  
  OBJECTIVE
  To study seroconversion and the magnitude of IgG responses in a SARS cohort with different disease severities.
  
  
  METHODS
  A retrospective analysis of all acute and convalescent-phase sera collected from a cohort of laboratory-confirmed SARS cases. Anti-SARS-CoV IgG antibody was detected using indirect immunofluorescence technique and quantified by two-fold serial dilutions. Characteristics of patients who seroconverted "early" (<median interval) were compared to those documented to remain sero-negative during the same time interval. Median IgG levels in convalescent-phase sera (collected within 30 days) were compared among patients with different disease severities. Correlations between IgG levels and important laboratory parameters were assessed.
  
  
  RESULTS
  A total of 325 laboratory-confirmed SARS cases were analyzed; of which 301 (92.6%) had anti-SARS-CoV IgG detected in their sera at the time of sampling. IgG was first detected on day 4 of illness; seroconversion occurred at a median of 16 days (range 4-35 days), and IgG peak levels were reached in the fourth week. Early seroconversion (<day 16) occurred more frequently among patients who required ICU-admission (chi2; p=0.011). Higher IgG levels were detected in patients who required supplemental oxygen (Mann-Whitney; p=0.002), ICU-admission (p=0.001), had negative pre-discharge fecal RT-PCR results (p=0.004), and lymphopenia at presentation (p=0.028). Peak IgG titres also correlated positively with peak LDH levels (Spearman's r=+0.360; p<0.001) among survivors.
  
  
  CONCLUSIONS
  Severe SARS is associated with a more robust IgG response.
authors.affiliation: Department of Medicine and Therapeutics, Prince of Wales Hospital, Faculty of Medicine, The Chinese University of Hong Kong, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, PR China.
authors.forename: Nelson
authors.initials: N
authors.lastname: Lee
authors.forename: P K S
authors.initials: PK
authors.lastname: Chan
authors.forename: Margaret
authors.initials: M
authors.lastname: Ip
authors.forename: Eric
authors.initials: E
authors.lastname: Wong
authors.forename: Jenny
authors.initials: J
authors.lastname: Ho
authors.forename: Catherine
authors.initials: C
authors.lastname: Ho
authors.forename: C S
authors.initials: CS
authors.lastname: Cockram
authors.forename: David S
authors.initials: DS
authors.lastname: Hui
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000097:blood; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D045473:Severe acute respiratory syndrome-related coronavirus / Q000276:immunology*; D045169:Severe Acute Respiratory Syndrome / Q000097:blood* / Q000276:immunology; D012720:Severity of Illness Index
chemical_list: D000914:Antibodies, Viral; D007074:Immunoglobulin G