SUMMARYWe systematically reviewed the current understanding of human population immunity against SARS-CoV in different groups, settings and geography. Our meta-analysis, which included all identified studies except those on wild animal handlers, yielded an overall seroprevalence of 0 . 10% [95% confidence interval (CI) 0 . 02-0 . 18]. Health-care workers and others who had close contact with SARS patients had a slightly higher degree of seroconversion (0 . 23%, 95 % CI 0 . 02-0 . 45) compared to healthy blood donors, others from the general community or non-SARS patients recruited from the health-care setting (0 . 16%, 95% CI 0-0 . 37). When analysed by the two broad classes of testing procedures, it is clear that serial confirmatory test protocols resulted in a much lower estimate (0 . 050%, 95 % CI 0-0 . 15) than single test protocols (0 . 20 %, 95% CI 0 . 06-0 . 34). Potential epidemiological and laboratory pitfalls are also discussed as they may give rise to false or inconsistent results in measuring the seroprevalence of IgG antibodies to SARS-CoV.

Eight general practitioners had severe acute respiratory distress syndrome (SARS) in Hong Kong during the epidemic, and others may have been infected by the SARS coronavirus without developing the full syndrome. We conducted a serological and questionnaire survey to determine the prevalence of subclinical infection by SARS coronavirus among general practitioners in Hong Kong. Participants had to be doctors actively practising in family medicine and who did not have SARS. Approximately 3200 general practitioners were invited to participate and the results of 574 were eligible for analysis. 29 samples were tested positive by enzyme-linked immunosorbent assay, but all these samples had titre < 25 by immunoflorescence assay. The prevalence for seropositivity was thus 0% (95% CI, 0.0%-0.6%). This finding documents the lack of subclinical infection by SARS coronavirus in an at-risk group in the community.

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The practice of grouping within a standard isolation room is recommended to continue in the future. Moreover, intensive infection control training for all staff is of highest importance to safeguard the health of both staff and patient.