Biomedical Engineering Reference
In-Depth Information
many authorities, including the World Health Organization (WHO) and the
Centers for Disease Control and Prevention (CDC), have warned of the pos-
sible re-emergence of this highly infectious disease. Thus, the sensitive tests
for SARS are of great public health importance. However, a number of diag-
nostic tests are not very sensitive during the early phase of the disease. For
instance, the use of nasopharyngeal aspirates using an early generation reverse-
transcription polymerase chain reaction (RT-PCR) for SARS-CoV has a sensi-
tivity of only 32% on d 3 of the disease
(
7
)
. This severe limitation has restricted
our ability to identify patients in a prompt manner and to institute isolation and
treatment.
Based on the publicly released full genomic sequences of SARS-CoV
(
8-10
)
,
various molecular detection methods based on RT-PCR have been developed.
These PCR-based diagnostic tests are used to detect SARS-CoV RNA in
patients' specimens in which viral RNA is reverse-transcribed into DNA and
then different regions of the SARS-CoV genome are specifically amplified by
PCR. Several RT-PCR protocols developed by members of the WHO labora-
tory network are available on the WHO website
(http://www.who.int/csr/sars/
RT-PCR is mainly divided into qualitative (conventional) and quantitative
approaches. Conventional RT-PCR approaches are normally qualitative in
nature and require
time-consuming and contamination-prone post-PCR analy-
sis. Real-time quantitative RT-PCR has overcome many of these shortcomings
and has been increasingly adopted by various laboratories for SARS diagnosis
(
2
,
11-15
)
. With suitable instrumentation, this technology allows data to be
recorded and analyzed during PCR cycling. Furthermore, it runs as a closed-
tube system, and postamplification manipulation can be eliminated. Thus, this
methodology reduces the risk of contamination and minimizes hands-on time.
The entire amplification process requires only 3 h and allows such technology
to be used for high-throughput application.
During the SARS outbreak, the PCR-based testing for SARS was focused
mainly on the analysis of nasopharyngeal aspirates, urine, and stools
(
7
,
11
)
.
An early study reported that SARS-CoV RNA was detected in 32% of
nasopharyngeal aspirates from SARS patients studied at a mean of 3.2 d after
the onset of illness, and the detection rate increased to 68% at d 14
(
7
)
. In the
same study, SARS-CoV RNA was detected in 97% of stool samples collected
at a mean of 14.2 d after symptom onset. Similarly, viral RNA was detected in
42% of urine samples collected from the SARS patients at a mean of 15.2 d
after onset
(
7
)
. Despite the high sensitivity of stool sample testing, early detec-
tion of SARS-CoV still suffers from a lack of high sensitivity. Although most
of the assays have been predominantly focused on RNA extracted from
nasopharyngeal aspirates, urine, and stools, the quantitative interpretation of
