In addition to being the standard testing method for the diagnosis of COVID-19, the nasopharyngeal swab is also frequently used for the detection of various viruses and bacterial infections.
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This article will provide information on how the nasopharyngeal swab is correctly performed, how samples obtained from the swab are analyzed, and what diseases aside from COVID-19 can be diagnosed by this method.
How is a nasopharyngeal swab performed?
Before any type of diagnostic testing can be performed, healthcare professionals must perform these tests in a specialized and sterilized room that prevents the spread of the virus.
All healthcare professionals administering the nasopharyngeal swab test must wear the recommended personal protective equipment (PPE), of which should include an N95 mask, disposable cap, goggles, gown, latex gloves, and shoe covers.
The nasopharyngeal swab must be performed when the patient sitting upright and their head in a straight position, as this provides easy visibility and access to the nasal floor, which is perpendicular to the center axis of the patient’s face.
The swab is inserted into the patient’s nose and is aimed in a parallel direction to the nasal and septum floor. As long as there are no obstructions present within the nasal cavity, the swab will continue to move in this direction until it reaches the nasopharynx, at which point resistance will be felt by the testing personnel.
Once the swab reaches the nasopharynx, it is recommended that it is rotated gently and completes two complete 360-degree rotations to allow the secretions from this area to be absorbed.
Once the swab is removed from the patient’s nose, it is immediately inserted into a vial that contains culture media. The swab handle that extends past the opening of the vial is snapped off to allow the tube to be closed.
What can be detected by a nasopharyngeal swab?
As previously mentioned, a nasopharyngeal swab is widely used to diagnose active SARS-Cov-2 infection, which is the virus that often results in the disease commonly known as COVID-19.
Several different upper and lower respiratory tract viruses can also be detected through nasopharyngeal swabs, some of which include rhinovirus, adenovirus, influenza, respiratory syncytial virus (RSV), human parainfluenza viruses (HPIV), human metapneumovirus (HMPV) and non-polio enterovirus (EV).
Since the nasopharynx is normally home to a high number of both nonpathogenic and pathogenic bacteria, this testing method can also be used to diagnose certain bacterial pathogens, such as Streptococcus pneumoniae, Haemophilus influenza, and Moraxella catarrhalis.
Notably, the convenience of a nasopharyngeal swab for diagnostic purposes has inspired researchers to develop non-invasive tests for several unexpected health conditions. California based diagnostics company Veracyte, for example, has recently introduced a novel nasal swab that collects nasal epithelial cells for the early molecular detection of lung cancer in both current and former smokers.
Similarly, researchers from the Chang Gung Memorial Hospital in Taiwan have utilized this sampling technique to assess its usefulness in the molecular diagnosis of nasopharyngeal carcinoma (NPC).
Methods for analyzing nasopharyngeal swab samples
The current standard for diagnosing SARS-CoV-2 once a nasopharyngeal swab has been obtained is the real-time fluorescence-based polymerase chain reaction (RT-PCR).
Typically, the RT-PCR test will measure several different RNA gene targets, such as one or more of the envelope (env), nucleocapsid (N), spike (S), RNA-dependent RNA polymerase (RdRp) and ORF1 genes.
RT-PCR is considered to be an ideal analytical technique for SARS-CoV-2 detection due to its reliability, low cost, and sensitivity, particularly when compared to alternative diagnostic approaches like cell culture, antigen detection, and serological methods.
Preventing false negatives
An incorrectly performed nasopharyngeal swab can lead to a greater likelihood that a patient receives a false-negative test result. False-negative results are important issues to address, as these results can cause patients who are positive for certain illnesses to spread highly contagious diseases, particularly COVID-19, to many other individuals unknowingly.
There are several reasons why negative test results can arise as a result of an improper nasopharyngeal swab method. One example includes the various locations between the opening of the nose and the nasopharynx that the testing personnel can encounter resistance.
If the healthcare professional feels resistance almost immediately after placing the swab in the patient’s nose, the nasal sill has likely been hit, which indicates that the swab must instead be aimed slightly higher to rise above this tissue. Additional locations where resistance can be met before arriving at the nasopharynx include the inferior turbinate and the anterior face of the sphenoid sinus.
Typically, an experienced caregiver can recognize when the test swab has reached 9-10 centimeters into the nasal cavity. If the swab does not reach this depth, it has not accurately sampled fluid from the nasopharynx and can therefore not adequately determine the presence of a disease within this location of the body.
It is therefore critical for testing personnel to be adequately trained on how to reliably perform a nasopharyngeal swab test.
References and Further Reading
- Pondaevn-Letourmy, S., Alvin, F., Boumghit, Y., & Simon, F. (2020). How to perform a nasopharyngeal swab in adults and children in the COVID-19 era. European Annals of Otorhinolaryngology, Head, and Neck Diseases. doi:10.1016/j.anorl.2020.06.001.
- Kaufmann, A. C., Brewster, R., Rajasekaran, K. (2020). How to perform a nasopharyngeal swab – an otolaryngology perspective. The American Journal of Medicine. doi:10.1016/j.amjmed.2020.05.004.
- Li, L., Chen, Q., Li, Y., Wang, Y., Yang, Z., & Zhong, N. (2013). Comparison among nasopharyngeal swab, nasal wash, and oropharyngeal swab for respiratory virus detection in adults with acute pharyngitis. BMC Infectious Diseases 13(281). doi:10.1186/1471-2334-13-281.
- Rawlings, B. A., Higgins, T. S., & Han, J. K. (2013). Bacterial pathogens in the nasopharynx, nasal cavity, and osteomeatal complex during wellness and viral infection. American Journal of Rhinology & Allergy 27(1); 39-42. doi:10.2500/ajra.2013.27.3835.
- Sethuraman, N., Jeremiah, S. S., & Ryo, A. (2020). Interpreting Diagnostic Tests for SARS-CoV-2. Journal of the American Medical Association. doi:10.1001/jama.2020.8259.
- Hao, S., Tsang, N., Chang, K., & Ueng, S. (2004). Molecular diagnosis of nasopharyngeal carcinoma: Detecting LMP-1 and EBNA by nasopharyngeal swab. Otolaryngology-Head and Neck Surgery 131(5); 651-654. doi:10.1016/j,otohns.2004.04.013.
- “Post T144 – Lung Cancer Detection Via Whole-Transcriptome RNA Sequencing of Nasal Epithelium” – Veracyte