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.