CONCLUSION
Overall, aggregate studies suggest that lower respiratory tract
specimens, especially BAL, tend to give a higher diagnostic yield than
upper respiratory specimens in patients with pneumonia and should
therefore be obtained whenever possible. However, lower respiratory
sampling involves greater technical difficulty and exposure risk. BAL is
also unacceptable as a screening tool. Hence, upper respiratory sampling
remains highly relevant even though current literature increasingly
highlights NS/NPS’s and OPS’s limitations and possible false negative
results. A false negative result allows the release of an infected
patient back into the community for continued viral transmission. From a
public health perspective, patients who have symptomatology of
SARS-CoV-2 but who tested negative initially, should be tested again and
asked to be isolated at home. It is critical for clinicians to base
their diagnosis on more than one test, and to consider the patient’s
risk susceptibility especially in the setting of known community spread.
At present, the United States Centers for Disease Control and Prevention
(CDC) recommends that nasopharyngeal and oropharyngeal flocked swabs
should be used for collection of specimen for SARS-CoV-2 viral
detection.26 While these methods have their
limitations, both allow rapid up-scaling for mass testing and detection,
as part of most countries’ greater strategy to proactively test, isolate
and contact-trace infected cases. Lower respiratory sampling methods
lack rapid up-scaling potential.
The SARS-CoV-2 virus demonstrates affinity to angiotensin-converting
enzyme 2 (ACE2) receptor which is present in respiratory mucosa, heart,
kidney, endothelium, and intestine tissues.27-28 As
such, numerous other biological sampling methods such as, but not
limited to, blood, urine and fecal specimen collection have been
described. The in-depth discussion of each is beyond the scope of this
article. Further aggregate studies may be considered to examine the
diagnostic capability of each of the abovementioned methods.