Correspondence
Detection of SARS Coronavirus in Plasma by Real-Time RT-PCR
N Engl J Med 2003; 349:2468-2469December 18, 2003
- Article
To the Editor:
The identification and sequencing of a novel coronavirus1 associated with the recently described severe acute respiratory syndrome (SARS)2 have permitted the development of antibody-based and genome-based tests for the infection.3,4 Although antibody seroconversion provides reliable proof of infection, it is not suitable for early diagnosis. Techniques for genome detection have the potential to provide earlier diagnosis, but the sensitivity of genome-based tests of respiratory samples such as nasal and throat swabs is likely to be low in patients presenting early with fever alone, before the development of respiratory symptoms. We therefore investigated the potential of genome detection in blood to provide a diagnosis during this very early phase.
A total of 65 plasma samples obtained within 10 days after the onset of fever were available from 26 patients with SARS at the Prince of Wales Hospital, Hong Kong. All patients met the World Health Organization's case definition and had seroconversion or a fourfold increase in antibody to the SARS-associated coronavirus (SARS-CoV), as measured by immunofluorescence. Viral RNA was extracted and amplified by means of a nested reverse-transcriptase polymerase chain reaction (RT-PCR), with the use of both qualitative and quantitative real-time assays (ABI Prism 7000 system) and the primer sets described by Drosten et al.4 Full details of the assay protocols are available as Supplementary Appendix 1 with the full text of this letter at www.nejm.org.
The rate of detection of SARS-CoV RNA in the 24 patients tested within three days after the onset of fever was 79 percent (detection in 19 of the 24 patients). Between 3 and 10 days after the onset of fever, no additional patients with viremia were identified with the use of either the qualitative or the quantitative assay (Figure 1AFigure 1
Detection of Severe Acute Respiratory Syndrome (SARS)–Associated Coronavirus with a Reverse-Transcriptase Polymerase-Chain-Reaction (PCR) Assay (Panel A) and Changes in the Viral Load (Panel B) in Plasma Samples Obtained up to 10 Days after the Onset of Fever in 26 Patients.). In the 19 patients in whom the viral genome could be quantified on one or more occasions, the plasma viremia level rose early and was maximal at around day 4 or 5 after the onset of fever (Figure 1B). The viral load then decreased in most patients, though it remained detectable at a low level in four of the five patients from whom samples were obtained on either day 9 or day 10.The detection sensitivity of 79 percent within the first three days is better than the reported rate for nasal and throat swabs and is equivalent to that for nasopharyngeal aspirates.3 With the current protocol, RNA from only 70 μl of plasma was analyzed, and it is likely that centrifugation of a larger volume of plasma would increase the detection sensitivity. The use of plasma viremia for diagnosing SARS-CoV infection also has the advantage of not requiring nasopharyngeal aspiration, which is regarded as a risk-prone procedure.5
5 ReferencesPaul R. Grant, Ph.D.
Jeremy A. Garson, M.D., Ph.D.
Richard S. Tedder, F.R.C.P., F.R.C.Path.
Royal Free and University College Medical School, London W1T 4JF, United Kingdom
paul.grant@ucl. ac. uk Paul K.S. Chan, M.D.
John S. Tam, Ph.D.
Joseph J.Y. Sung, M.D., Ph.D.
Prince of Wales Hospital, Shatin, NT, Hong Kong, China1
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Full Text | Web of Science | Medline5
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