NMDA Journal Winter 2020-21

18 New Mexico Dental Journal, Winter 2020-21 S ince the start of the pandemic, dentists, dental specialists and hygienists have been at the top of the list of health professionals most vulnerable to contracting COVID-19. As we gained more knowledge about COVID-19’s livelihood and transmissibility, it was natural to seek as many methods as possible to pre- vent community spread of the virus. A key step in prevention is to know who has the virus. Therefore, having methods to test patients was of utmost importance. In general, dental offices across the country need a test that is accurate and quick. Ide- ally, a test that can provide results within minutes of a patient’s scheduled appoint- ment would be most beneficial for all dental offices. Once these types of tests are avail- able, they will be the next best preventive measure for dental professionals to take until a COVID-19 vaccine is distributed. This article explores the different types of tests with more discussion on antigen or point-of- care tests. In the end, a brief overview of Clin- ical Laboratory Improvement Amendments (CLIA) will be discussed. Coronavirus Microbiology To understand how the SARS-CoV-2 tests work, it is important that we also understand the basic microbiology of coronaviruses. COVID- 19, as well as other coronaviruses, has a struc- ture that is spherical. It contains “single- stranded (positive sense) RNA” within its par- ticles and the outside has “club-shaped gly- coprotein projections.” The glycoprotein structures are what allow the virus to attach to the host cell. Once attached to the host cell, the “uncoated genome is transcribed and translated,” and eventually new virions are formed and budded from the host cell membranes (Tyrrell & Myint 1996). Coronaviruses are also very meticulous and tend to grow only in “differentiated respira- tory epithelial cells.” The virus creates cell damage and this in turn causes localized inflammation. Body responses to the inflam- matory response are increased mucus pro- duction, sneezing, airway obstruction, and increased temperature of the mucosa. As we have found, some individuals are asymptom- atic, but they still are infected (Tyrrell & Myint 1996). This is one of the many reasons testing for COVID-19 is so important, it is difficult to differentiate among the symptomatic and asymptomatic individuals. SARS-CoV-2 Test Types The tests available are organized into 3 cate- gories: Serology (Antibody), Molecular, and Antigen. In general, the molecular and anti- gen tests will show who has a current/active infection. The serology test will show who had a past infection. The molecular test is currently considered the “Gold Standard.” All three of the test types will be discussed in the following paragraphs. Serology Testing A serology test is a blood test. It is an “Enzyme-Linked Immunosorbent Assay (ELISA)-based test external icon to detect SARS-CoV-2 antibodies in serum or plasma components of blood.” The ELISA test uses purified SARS-CoV-2 protein (not a live virus) as antigen. The test is designed to prevent cross-reactivity with other common corona- viruses, like the common cold, but it is possi- ble for cross-reactivity to happen. The CDC’s serologic test is greater than 99 percent spe- cific and 96 percent sensitive, and it can detect infections that occurred in people 1 to 3 weeks earlier (cdc.org) . Completing an antibody or serology test on a dental patient is of no use to dental profes- sionals, but it is useful for epidemiology pur- poses. Researchers are able to better evaluate the transmission dynamic of the virus and, thus, can provide recommenda- tions to key community leaders and govern- ment officials on how the virus is spreading. Data can also be gathered to calculate prob- abilities of re-infection, thereby allowing us to determine if immunity is possible and how long the immunity will last. Molecular Testing Molecular testing detects an active infection. Molecular testing does this by identifying genetic material or unique markers of the pathogen itself. Genetic material of SARS- CoV-2 is RNA, and this remains in the body as the virus is replicating. Samples that are obtained for this test are nasopharyngeal swabs or saliva. Other bodily material can be used like feces, urine, and blood, but with COVID-19, the nasopharyngeal swabs are the most reliable. When someone has a flu, it is found that viral material concentrates in the nasopharyngeal region early on in an active infection. Molecular tests work by using a process of real-time reverse transcriptase quantitative polymerase chain reaction (rRT-PCR). Some tests use a qPCR, which means the test pro- vides quantitative information, not just quali- tative data. The PCR on its own is qualitative, and gives a basic “yes or no” answer regard- ing the presence of COVID-19. In both rRT- PCR and qPCR there are three basic steps: 1. The test identifies genetic material, DNA or RNA, of the pathogen with the use of “primers.” Primers are small pieces of single- stranded DNA chemically synthesized in the lab. The primers match to a specific region of the parent DNA and “attach or anneal.” Then an amplification process starts, the nucleic acid molecule is enzy- matically copied over and over to make a progeny population with same sequence as the parent. For viral RNA-based genomes, the additional step of reverse transcriptase is needed. 2. The amplification process is repeated in cycles to closely mimic the natural DNA replication processes in human cells. To complete this natural DNA replication, the PCR assays rely on a programmed temperature change to allow the DNA to split apart. Therefore, thermocyclers are needed. Exceptions to the thermocy- clers are isothermal methods like loop- mediated isothermal amplification (LAMP), which do not require heated cycles to amplify the target DNA. How- ever, the primer design for RT-LAMP must be exact or it will not work. TESTING FOR COVID-19 continues on page 20 