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be modified to target any genetic sequence—for example, that sputum was most accurate, followed by nasal swabs
targeting two regions in the genome, one that is unique to for detecting SARS-CoV-2 RNA. While sputum, nasal,
SARS-CoV-2 and one that is common to all SARS-like and throat swabs revealed positive results, after eight days,
coronaviruses. This ensures the assay is distinguishing the positive rate for throat swabs was much lower. A
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between SARS-CoV-2 and closely related viruses. The test more recent study showed that saliva from the posterior
also decreases turnaround time by cutting a four-hour- oropharynx (coughed up by clearing the throat), especially
long assay down to 45 minutes, thus improving the speed first thing in the morning after being supine all night, also
of diagnosis. 12 produced high yield samples that mirrored endotracheal
aspirates. Notably, the non-invasive nature of saliva
Point-of-Care Tests collection may be more acceptable to patients requiring
Recently, a number of companies have been serial sampling. Currently, best evidence suggests that
7
developing rapid point-of-care (POC) tests that can detect when given a choice, sputum followed by nasal-pharyngeal
viral nucleic acids or viral proteins (antigens). Rapid POC (NP) swab and saliva (FDA approved on April 18, 2020)
tests that will make individual testing more readily are the preferred sample types. In addition to the type of
available are eagerly anticipated. The results of proper sample collected, proper methodology during sample
validation studies for these tests are essential before their collection is critical.
widespread adoption. RT-PCR is estimated to have up to a 30% false
A handheld DNA analyzer that automates nucleic negative rate for identifying viral RNA in an infected
acid extraction and amplification has recently been person. The majority of this is the result of collection
repurposed for SARS-CoV-2 detection. It provides procedures that use inappropriate sites or collect
results in approximately one hour and can be used at inadequate amounts of material. Collection outside the
point-of-care locations. It has been approved by Health diagnostic window (3-21 days after exposure) can also
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Canada but is not yet widely available. Another single increase the false negative rate. Handling, transport, and
use disposable machine that can perform 40 cycles of storage of swabs as well as the presence of interfering
PCR in seven minutes giving an easy to read qualitative substances or contamination also play a role in the false
result is also in the final stages of development. If negative rate. 16
validated these technologies may facilitate the need for One study showed that the titers of viral RNA tend to
creating easily accessible testing with rapid turn around peak at or just before symptom onset followed by a rapid
times. decrease in the naso- and oropharynx and a gradual
Lateral flow immunoassays that can detect various decrease in sputum and stool. Titers remain high,
SARS-CoV-2 proteins have also been developed. The especially in the sputum and stool, even after symptoms
lateral flow assay is similar to a home pregnancy kit in resolve. This begs the question as to whether the presence
3
which “capture reagents,” such as monoclonal antibodies of viral RNA in a sample equates to infectious viral
(mAbs), are directed at a viral antigen and are immobilized shedding. The answer appears to be “No,” since it was
at defined locations on a nitrocellulose membrane along shown that even though stool samples can contain high
with labeled detector mAbs to the same target. Binding amounts of viral RNA, infectious viral particles grown in
between the analyte (viral protein or RNA in sample) and culture have not been isolated from stool. Even though
3
the capture and detector mAbs reveals a positive test by the presence of viral RNA is not perfectly correlated with
producing a visible colored line. 11 infectious viral shedding, it is prudent to assume that a
patient with a positive respiratory RT-PCR test is
Viral Culture contagious and should observe appropriate quarantine
Assessing the ability of the virus collected from a measures.
sample to grow in culture can determine whether the
sample contains infectious viral particles as opposed to Regulations
only viral RNA. These assays are time consuming and Labs performing viral RNA testing must have
require labs with high-level biohazard containment emergency use authorization (EUA) from the FDA and
facilities and are best reserved for research purposes. should have CLIA certification for high complexity
testing. Since there are a large number of labs offering
Sample Collection testing, it is important to ensure they are meeting
The accuracy of results using viral detection tests are appropriate regulatory guidelines. Currently, all POC
most often contingent on the type of sample being tested testing must be done in a CLIA-certified lab (https://
and the methodology of collection. Viral RNA can be www.cdc.gov/coronavirus/2019-nCoV/hcp/clinical-
extracted from all types of respiratory membranes, criteria.html).
including OP, nasal, and NP swabs; saliva; and sputum.
One smaller study found no difference in detection rates
between OP and NP, while another larger study found
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Messier—Primer on SARS-CoV-2 Testing Integrative Medicine • Vol. 19, No. S1 • Epub Ahead of Print 47