Anti-SARS-CoV IgG response in relation to disease severity of severe acute respiratory syndrome
Received 9 May 2005; received in revised form 7 July 2005; accepted 12 July 2005. published online 22 August 2005.
Abstract
Background
The association between a robust or depressed antibody response and clinical severity of SARS remains unknown.
Objectives
To study seroconversion and the magnitude of IgG responses in a SARS cohort with different disease severities.
Study design and method
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 (χ2; 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.
aDepartment 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, P.R. China
bDepartment of Microbiology and School of Public Health, Faculty of Medicine, The Chinese University of Hong Kong, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, P.R. China
cCentre for Epidemiology and Biostatistics, School of Public Health, The Chinese University of Hong Kong, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, P.R. China
ABSTRACT