Rapid Influenza testing in children and adults

Introduction
Influenza is, in basic terms, a viral attack on the respiratory system of an individual.  In most cases, it is simply referred to as the flu.  Some of the more common symptoms of influenza include, but they are not limited to, a sore throat, nasal congestion, weakness and fatigue, headache, muscle aches, and fever.  In as far as diagnosis is concerned, a physical exam is in most cases conducted alongside tests.  There are various tests that could be used in influenza diagnosis.  These could be inclusive of the rapid influenza diagnostic tests (RIDTs).  
Discussion
From the onset, it is important to note that according to the Centers for Disease Control and Prevention – CDC (2016), RIDTs “are immunoassays that can identify the presence of influenza A and B viral nucleoprotein antigens in respiratory specimens, and display the result in a qualitative way (positive vs. negative).”  As CDC further points out, these tests are commercially available in the U.S.  Examples of RIDTs could be inclusive of enzyme-linked immunosorbent assays and immunochromatographic tests.  Due to their rapidity (i.e. rapidly available results) and ease of use, RIDTs are in most instances deployed at the point-of-care.   
During outbreaks of institutional respiratory diseases, RIDTs have in the past come in handy in as far as the identification of influenza is concerned.  Thanks to RIDTs authorities can act with speed to contain influenza – specifically via the advancement of prophylactic treatment to persons who despite presenting no flu symptoms have been exposed to virus (Peci, Winter, King, Blair, and Gubbay, 2014).  It should also be noted that as Peci, Winter, King, Blair, and Gubbay (2014) further point out, during outbreaks, RIDTs make it possible for “antivirals to be rapidly administered to patients” as one way of containing the said outbreaks (4310).    
There are various samples which could be utilized for RIDTs.  These are inclusive of tracheal washings or aspirate, as well as nasopharyngeal secretions and other respiratory specimens.  Specific optical signals, i.e. color change, are used to signal viral antigen presence (World Health Organization, 2018).  According to WHO, “the most common antigen target in commercially available pan-influenza6, influenza A, influenza B, or combination influenza A and B tests is nucleoprotein (NP)” (WHO, 2018, p. 11).  It would also be prudent to point out that RIDTs are often available in various formats.  Some of the formats identified by WHO include cards, cassettes, and dipsticks.   
The specificity of RIDTs happens to be rather high.  For seasonal influenza, the World Health Organization observes that specificity could be in the range of 90 to 100 percent.  On this front, “while false positive results can occur, they are uncommon when influenza viruses are circulating locally” (WHO, 2018, p. 15).   Although the time frame within which RIDTs yield results (i.e. <15 minutes) could be deemed relevant from a clinical perspective, the sensitivity of RIDTs when applied to respiratory specimens in an attempt to detect influenza viruses happens to be limited.  This, according to CDC (2016), is in comparison to viral culture or RP-PCR.  Thus, according to CDC (2016), negative test results of RIDTs ought to be “interpreted with caution given the potential for false negative results, especially during peak influenza activity in a community.”  It should also be noted that apart from false negatives, there is also a significant probability for false positive results.  This, according to CDC, is more so the case during those periods whereby there is low influenza activity.  Peci, Winter, King, Blair, and Gubbay (2014) also observe that there are a wide range of factors which influence the specificity as well as sensitivity of RIDTs.  These, in the words of the authors, are inclusive of “the influenza virus type and subtype, the body site from which the specimen was collected (e.g., nasopharyngeal versus throat swab), the time to specimen collection, and patient age” (Peci, Winter, King, Blair, and Gubbay, 2014, p. 4312).  
On the basis of the findings highlighted above, it clear that RIDTs may have a few key limitations as clinical decision making tools.  As a consequence, in those instances whereby influenza immunofluorescence assays or RT-PCR are available, RIDTs ought not to be used especially when dealing with hospitalized patients (Cantle, Thenabadu, and Lacy, 2015).  There are also some factors that should be taken into consideration in seeking to ensure that the performance of RIDTs is optimized.  These include ensuring that the collection of specimen is undertaken “during the window of time in which the patient is likely to be replicating virus to sufficient titers that antigen can be detected” (Atkinson and Mabey, 2019, p. 73).  There is also need to ensure that the collection of specimen is undertaken by health workers who are well-trained.   
Conclusion
In the final analysis, it should be noted that the utilization of RIDTs does have its own advantages and disadvantages.  In addition to being relatively simple to perform, the time frame within which RIDTs yield results is largely relevant from a clinical perspective.  However, as it has been pointed out in the text above, these tests have a significant potential to return false negative results.  This is more so the case during periods of high influenza activity.  Thus, in as much as RIDTs are beneficial and especially convenient in the identification of influenza during institutional disease outbreaks, we must be aware of the various limitations highlighted above so as to further promote their effectiveness.     
References
Atkinson, K. & Mabey, D. (Eds.). (2019). Revolutionizing Tropical Medicine: Point-of-Care Tests, New Imaging Technologies and Digital Health. Hoboken, NJ: John Wiley & Sons. 
Cantle, F., Thenabadu, S. & Lacy, C. (Eds.). (2015). Challenging Concepts in Emergency Medicine: Cases with Expert Commentary. New York, NY: Oxford University Press.
Centers for Disease Control and Prevention – CDC (2016). Rapid Influenza Diagnostic Tests. Retrieved from https://www.cdc.gov/flu/professionals/diagnosis/clinician_guidance_ridt.htm
Peci, A., Winter, A., King, E., Blair, J. & Gubbay, J. (2014). Performance of Rapid Influenza Diagnostic Testing in Outbreak Settings. J Clin Microbiol, 52(12), 4309-4317. 
World Health Organization (2018). Use of Influenza Rapid Diagnostic Tests.  Retrieved from https://apps.who.int/iris/bitstream/handle/10665/44304/9789241599283_eng.pdf?sequence=1