Testing for Covid-19 has become one of the most reported metrics of the pandemic.
Governments proudly publish their national number of tests, giving the public hope that something proactive is being done. But as it turns out, this hope is based on the
expectations that the testing process is an accurate process. In this post, Dr. Mark takes a sharp scalpel to Covid-19 testing. If you are a manager of a workforce, or simply perhaps you are considering taking the test for your winter sniffles, read on.
Managers Wanting PCR Covid Testing on Staff:
Before considering the polymerize chain reaction (PCR) test as a silver bullet to keeping your workforce safe then consider the following:
- The current test is of no value unless Covid-19 symptoms are present in your employee (Find a description of the symptoms here). You should quarantine staff members who have been in contact with a confirmed case and wait for their symptoms to develop before you test them. The diagnosis will be clinically obvious at this stage, so testing shouldn’t be necessary. The clinical opinion of your doctor will be of more value here than an unreliable test.
- If you insist on a test, then you will be adding to the delay in the current testing backlog.
- If you still want a test knowing the above, then you pay for it (not medical aid) R850.00 and interpret it as you blindly see fit. At this point management specialists will remind you of the GIGO principle – garbage in garbage out. As this test will be negative, to get a true status you will need to retest your employee after a week. Rather give them R1700 ($98) and send them home for a week to wait for symptoms. Don’t bother me unless there are symptoms.
- Laboratories conducting tests on people off the street, without screening are not helping the situation for the above reasons. And yes, to confuse matters we are seeing false positives as well in persons who are healthy and uninfected. They wouldn’t have been sent for a test if they were properly screened.
- Current guidelines are that people under the age of 55 need not be tested. Quarantine them if they have symptoms.
COVID tests explained
You just can’t trust a negative person. Up to 29% of people who get the all-clear from a COVID test are likely infected with the virus. This means that a lot of highly contagious people are moving around confident they’re safe and trusted as contagion-free by the people they connect with. But they’re ignorant Trojan Horse’s for the virile Corona foe.
It’s not their fault. The absence of a screening test for the Corona Virus is to blame. The current test used is a specific test which ideally should be used to validate a screening test. This test is not only unreliable but the confusing statistical speak used by the testing profession helps to muddy the waters greatly. For example, a specific test is to rule out people who don’t have the infection, a negative here means that there are going to be more false positives. Confused? Don’t worry, even doctors battle here.
What we need for screening but don’t have is a sensitive test
A sensitive test should be cheap and easy to do. For example, the magnetic doorframe at the airport security will pick up any metal on your person. We have all experienced this problem, if the alarm resounds after you have removed your belt and car-keys then you are subjected to a specific test. This would more than likely include an X-ray or body-cavity search (not cheap and also unpleasant).
So, a sensitive test is prone to false alarms which we know will happen, but importantly, it gives us reassurance that there are no false negatives, i.e. no guns. We don’t start with a cavity search at the airport.
Medical examples of these sensitive tests are Mammograms, PSA (Prostate Cancer) tests, and HIV tests which all over-diagnose conditions. If negative, we can be fairly sure that they are negative. But if positive, uncomfortable tests such as a biopsy of your breast, prostate, or expensive HIV test must be done to confirm or rule out the bad news.
The problem with Coronavirus is that the only test giving rapid results is a moderately specific test and yes, it is uncomfortable, requiring a swab shoved 10cm up your nose. This test has a false negative rate of between 2% and 29%. What this means is that up to 29% of people who are told that they are negative may actually have the disease and are now free to roam around and infect the rest of us! The real value of this test is that if you have symptoms and you test positive then you are almost definitely positive. The test will usually only convert to positive about a week after contracting the illness. So, our problem is that we don’t have a screening test that is easy to do and are using the body cavity version to screen for the virus.
Dr Mark Holliday 27 June 2020