The pandemic of the novel coronavirus 2019 has changed the world and the way we are all living our lives. We have had to quickly adjust and face the challenges. To help during this crisis, I have been working on the frontlines of the Covid testing with a wonderful group of people. I have personally seen the anxiety, fearfulness, patience, and kindness of our human society. This experience has given me a different perspective especially since testing positive myself. I have gained a better understanding of the testing and I would like to share what I have learned. I believe we should all stay informed, especially when it comes to our health.
First off, let us talk about the Covid test. What is it? The Covid-19 test is a molecular test that detects the presence of viral RNA using a lab technique called polymerase chain reaction (PCR). A sample is collected by inserting a long swab into the nostril (nasopharyngeal swab), in the throat (oropharyngeal swab) or spitting into a tube to collect saliva. The sample is then sent off to the laboratory to be tested using an enzyme called reverse transcriptase. This enzyme changes the RNA into a matching piece of DNA. PCR then amplifies the DNA exponentially until it can be detectable with a help of a fluorescent signal. This is known as the cycle threshold (Ct Value), the number of amplification cycles necessary to detect the fluorescent signal. The CDC guidelines has set this number to less than or equal to 40. That means a sample must “light up” before or at 40 cycles to be positive. This is the threshold being` used in Montana’s state laboratory located in Helena. However, some experts believe such a cycle threshold is too sensitive and should be 30 to 35 (1). Even the CDC suggests it is difficult to detect a live virus with a threshold above 33 cycles. The 40 Ct value may have been helpful at the beginning of the pandemic. However, as the cases keep rising, it is important to catch the most transmissible people early on by using a test with a lower Ct value. It is therefore important that Ct values be reported with every positive test to help guide clinical and public health strategies (2).
What if you test positive? Are you infectious? From what we have just learned, the PCR test detects viral RNA, and it is unclear whether this represents an infectious virus. The gold standard to determine viral infectivity is by doing viral cultures. A viral culture is when a virus is injected into cell lines and observed for cell damage and death, which allows the release of new virus to infect other cells. From my discussion with our state laboratory, there is not any viral cultures being performed. A viral culture is time-consuming and performing one on every person being tested would be difficult. In my clinical opinion, a viral culture should be performed randomly from samples that tested positive at a lower cycle threshold. We should not be assuming that everyone who tests positive is infectious. This assumption helps protect the most vulnerable, but it is also greatly impacting our population and economy. As positive cases keep rising, more restrictions have been placed on the population. As reported in the Montana Standard on Oct. 18th of 2020, “100,000 Montanans in October alone had to stay home to isolate or quarantine, putting the state’s workforce capacity at risk”. Missing work has resulted in more families living below the poverty line, and many small businesses to be permanently closed.
What can we do to help drive this pandemic practically to zero? More restrictions may be helpful, but it is important we also take a better look at our testing procedures and make changes when necessary. If you test positive and have symptoms, please seek out care from your healthcare practitioner and distance yourself from others. Remember keep a positive attitude and trust that your body has the ability to heal itself.
If you would like to read more, I encourage you to read the references I have given below. Please feel free to contact me for any concerns or questions.
- Mandavilli, Apoorva. (2020, Aug 30). Your coronavirus test is Positive. Maybe it shouldn’t be. New York Times. https://www.nytimes.com/2020/08/29/health/coronavirus-testing.html
- Michael R Tom, Michael J Mina, To Interpret the SARS-CoV-2 Test, Consider the Cycle Threshold Value, Clinical Infectious Diseases, , ciaa619, https://doi.org/10.1093/cid/ciaa619
- (2020, Sept 17). PCR positives: what do they mean? The Centre for Evidence-Based Medicine, University of Oxford. https://www.cebm.net/covid-19/pcr-positives-what-do-they-mean/