Is the COVID-19 Test Accurate?

Tenzin Gyaltsen (Get Well Clinic)

 

As Ontario transitions into Stage 3, the province’s COVID-19 testing capacity remains a crucial factor for the speed at which we reopen. Recent numbers may seem promising, coming in at the lowest we’ve seen in months, but how accurate actually are these results? In a recent study by researchers at Johns Hopkins University, COVID-19 test results were shown to be alarmingly inaccurate, particularly in the case of false negatives.

A false negative is defined as a test that comes out negative, but should have been positive. In the case of COVID-19, a false negative refers to a patient that tests negative for their RT-PCR test (Link), but actually does have the virus. It’s easy to imagine why false negative cases are especially dangerous, as sick individuals may feel free to operate and go about their business as they usually do, increasing the risk of community spread.

In the study by Kucirka et al., the probability of a false negative result varied widely, but depended largely on the amount of time after initial exposure that the test was taken. The false negative rate was reported as 100% at the moment of exposure (or Day 0), which may seem drastic but makes sense given the limitations of the test (Link). At this point, the virus would have virtually no time to replicate and so the chances of any viral genetic material being picked up by a cotton swab are little to none. As the days progressed and symptoms developed (around Day 5), the false negative rate decreased to a minimum of 20% (Day 8). Interestingly, after Day 8, the false negative rate began to increase steadily, from 21% on Day 9 to 66% on Day 21. Like the early days of the disease, these high numbers may also be due to the decreased presence of viral genetic material during the patient’s recovery phase.

It goes without saying that every study has its own limitations, but the numbers presented in this particular study warrant concern. If we’re to safely continue reopening the province, we should be confident in our testing capability and accuracy, but these findings suggest that the ubiquitous RT-PCR (cotton swab) test may not be enough. It’s not all bad news though. Using the data collected from this study (and similar studies), we may gain a better understanding of when the best time to test patients actually is (i.e. when the false-negative rate is the lowest). From the data presented, it seems like that optimal window is about 2–4 days after symptoms first appear.

There are a number of things we can we take away from this study. The foremost is that the false-negative rate of COVID-19 tests is much higher than one might think, which may lead to an underestimation of the actual number of total cases. If you are feeling sick and receive a negative test result, do not treat it as a definitive answer. Continue to self-isolate to keep the people closest to you safe, and seek medical guidance before taking further steps. If you’re hesitant or unable to to visit a clinic in-person, please contact us (either through the online chat system or call 416.508.5691) to book a virtual appointment!

Source:

Kucirka LM, et al. (2020) Variation in false-negative rate of reverse transcriptase polymerase chain reaction-based SARS-CoV-2 tests by time since exposure. Ann Intern Med. https://doi.org/10.7326/M20-1495

 

 

Pin It

How Does the COVID-19 Test Work?

Tenzen Gyaltsen (Get Well Clinic)

 

We’ve all seen the videos online. A gowned individual sticks a long cotton swab into the back of someone’s nose and twists it around for a few seconds. Their unfortunate victim winces with discomfort but is evidently fine once the swab is removed (although maybe a bit teary-eyed). But what happens to the swab and its mucosal contents and how do specialists distinguish a COVID-19-positive from a COVID-19-negative case? How accurate actually are these results?


Upon arrival to a testing lab, the contents of the swab will be extracted and subjected to a reverse transcription-polymerase chain reaction (RT-PCR) test. Firstly, the sample is subjected to a series of steps that removes unneeded molecules such as proteins and lipids so that only genetic material remains. In a COVID-19-positive patient, the remaining genetic material (called RNA) is likely made up mostly of the patient’s own RNA and, to a lesser extent, RNA from the COVID-19 virus.


The viral RNA must first be replicated, a process known as “amplification”, in order to be plentiful enough for detection. For amplification to occur, the RNA is converted to DNA using an enzyme (a handy biological molecule) called reverse transcriptase. The amplification process requires a number of biochemical reagents (ingredients), each aiding in amplification in different ways. Within this “master mix” of ingredients is found heat-resistant DNA polymerase, another enzyme, that is required to produce new copies of viral DNA from existing copies. In addition, dNTPs (nucleotides) are the building blocks of RNA and DNA, and must be added to the sample in order for DNA polymerase to build new DNA. Finally, specific DNA primers, genetic fragments that bind only to viral DNA, are added and serve as initiation sites at which DNA polymerase may operate. Of course, if no viral RNA/DNA are present (i.e. a COVID-19-negative patient), specific DNA primers will not bind and no amplification will occur.

Once the different reagents are added, the sample is placed within a PCR machine that facilitates amplification through a 3 step cycle: denaturation (strand separation), annealing (DNA primer binding) and extension (new DNA construction). Each of these steps occur optimally at a specific temperature which is maintained by the machine in order to properly replicate the viral DNA (if present). By adding a fluorescent (light-emitting) dye or probe that binds to the sample’s DNA, scientists can determine if viral DNA has been replicated based on levels of detected fluorescence. If a sample has greater fluorescence compared to a control (a sample with no viral DNA), it can then be said that the sample contains viral genetic material and that the patient is COVID-19-positive.


After visiting a designated Ontario testing centre, RT-PCR results should be posted online within approximately 2–4 days (this also includes emergency department visits). But how accurate are these results?

It goes without saying that while the world combats COVID-19, other diseases and medical conditions aren’t simply going to wait their own turn. If you would like to seek medical help from a doctor but are hesitant to visit a clinic in-person, please contact us (either through the online chat system or call us 416.508.5691) to book a virtual appointment!

 

 

Pin It

Why does my doctor not include Annual Physicals anymore?

 

There is evidence that annual complete physical checkups in healthy individual (with no symptoms) do not significantly improve their risk of disease or death. Since 2012, the Ontario government revamped the coverage for Annual Physicals by changing the definition to targeted screening of age-specific risks (now called a Periodic Health Visit), and reducing the payment to doctors by 30% for the visit. The time allowed for this visit has also been reduced since there is less amount of history, physical exam, and testing.

We also know that excessive medically unnecessary checking or testing can lead to false positive findings, incidental benign findings, anxiety, and  unneccessary further invasive investigation and treatment.

Therefore, OHIP does not cover an Annual Complete Physical Exam for healthy individuals anymore. Complete Physical Exams for academic, employment, travel, or volunteering are not OHIP covered.

So if your doctor says she doesn't do Complete Physicals or Annual Exams, but a short Periodic Health Visit, then you will now know why.

https://www.theglobeandmail.com/life/health-and-fitness/health-advisor/annual-health-check-ups-physicals-becoming-a-thing-of-the-past/article27996873/

Pin It

Online COVID-19 Assessment

https://covid19toronto.ca/

 

COVID-19 Assessment Centres

https://www.toronto.ca/home/covid-19/covid-19-health-advice/covid-19-assessment-centres/

 

Pin It

How to Prevent Getting Cancer

Newer HPV Vaccine prevents 90% of cervical cancers, anal cancers, and genital warts!

Gardasil-9 is better than original Gardasil.

 

 

Cancer is a scary word. We all know someone, a friend, family member, or co-worker who developed cancer. They go through difficult treatments like surgery, chemotherapy and radiation. Sometimes they die. We all fear getting cancer some day in our life. When you feel a little sensation in your body, do you often wonder if you might have cancer? Many people always end up going to family doctors and asking if they have cancer. It is a top reason why people request unnecessary imaging and tests, just to reassure themselves that they don't have cancer. We also always get asked questions about what kind of foods, or supplements to take to prevent getting cancer. Why wait until you have cancer to treat it, when you can prevent getting cancer in the first place?

 

What if we told you that there was a vaccine that prevents 90% of cervical cancers, anal cancers, and genital warts? Would you want to prevent getting cancer and avoid going through all that stress and anxiety in the first place? Gardasil-9 is an HPV vaccine that does just that! 90% on anything, even a school exam, is worth it!

 

Gardasil-9 has been shown to prevent approximately 90% of cervical cancers in women. It also prevents anal cancers in men. It also prevents ugly genital warts in men and women. Research has shown that it is HPV (human papilloma virus) infects human skin and mucosa and causes cellular changes which lead to cancer. Gardasil 9 trains the body's immune system to recognize and kill the top 9 strains of HPV (human papilloma virus 6, 11, 16, 18, 31, 33, 45, 52 and 58) that cause cervical cancer and genital warts. If your body can fight off the infection and kill the virus, then your body heals and doesn't develop cancer. Gardasil 9 is available at your family doctor's office, such as Get Well Clinic (416-508-5691).

What if you wanted to take your chances with cancer, how likely could you get HPV infection? 7 out of 10 people (who are sexually active) will get an HPV infection in their lifetime (75%). What if you are not "sexually active?" Think again, you don't need to be "sexually active" to get infected with HPV. (https://www.ncbi.nlm.nih.gov/pubmed/2256864)

What if you didn't have a cervix? Well, you can still be protected against 90% of anal cancers and genital warts! The HPV vaccine is also for boys and men, especially if you love your current or future partner!

There is another older version of HPV vaccine, called Gardasil that is available in Ontario, and given to all Gr 7 and 8 students in the schools. As you can tell from the number, it only covers 4 strains of HPV (2 strains which cause cervical cancer, and 2 strains that cause genital warts). It only prevents 70% of cervical cancers. Would you 70% or 90% on a school exam? In order to boost your protection up to 90%, we recommend students be re-immunized with the newer Gardasil-9 at Get Well Clinic. Grade 7 boys in Ontario only started getting Gardasil in 2015 (but this was the original 4-strain version only).

Other countries are starting to recongize the importance of preventing cancer with vaccines. Hong Kong had introduced Gardasil 9 in 2016, and many Chinese students were travelling to the territory for this vaccine. Mainland China recently approved Cervarix and original Gardasil (another HPV vaccine) in 2016/2017. However, Cervarix and original Gardasil only covers 2 strains of HPV (16, 18), and therefore is only offers 70% protection for cervical cancer, but no protection against the other strains that cause genital warts.

Gardasil-9 is better than original Gardasil.

Get 90% Protected from cervical cancer and genital warts!

 

Even if you get the HPV vaccine, women should still see their family doctor regularly for PAP test's (Women's Health Exam) to check for early signs of cervical abnormalities that may develop in to cancer. Getting the vaccine does NOT mean you can skip the PAP tests.

 

Gardasil-9 is a vaccine that is injected in to the shoulder muscle. There are 2 or 3 shots needed over a span of 6 months, depending of your age. Gardasil 9 is officially indicated for girls/women from 9 yr old to 45 yrs old, and for boys/men from 9 yrs old to 26 yrs old. It has been recommended by the Canadian NACI guidelines for any age and any gender. It is safe for older men and women, however, the research studies only studied the vaccine in the indicated age groups. Your doctor may still recommend it for you depending on your specific situation.

It is better to get it earlier than later. Getting the HPV vaccine earlier means you get protected sooner and more effectively, before you are exposed to all the strains of HPV in your lifetime.

If you got original Gardasil or Cervarix, you can still get Gardasil-9 safely and boost your immunity to 90%.

 

Get your HPV vaccine today at Get Well Clinic! Contact us to make an appointment. 416.508.5691.

 

References:

http://www.arhp.org/publications-and-resources/clinical-proceedings/Managing-HPV/Impact
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC145302/
https://www.ncbi.nlm.nih.gov/pubmed/2256864
http://www.gardasil.ca/what-is-gardasil.html

 

 

Pin It
Page 1 of 2