OVERVIEW OF CURRENT COVID-19 SWAB TEST METHODS

When administered correctly, high-sensitivity polymerase chain reaction (PCR) tests are almost 99.9% accurate in spotting infected samples. They can identify tiny quantities of genetic material. They do this by using specific bacteria to multiply the number of detectable viral antigens in a sample. The time it takes to complete the COVID swab test is dictated by the time it takes the bacteria to grow before being lysed and the amplified antigen extracted. The process is repeated, each time to amplify antigens to a measurable level detected by fluorescent chromatography. 

PCR tests require trained laboratory technicians, a specific bacterial growth environment, appropriate reagents, and expensive machinery. To provide results, the process from start to finish takes at least 2 laboratory time-hours. Transportation time to and from the laboratory and the time it takes to forward reports increases time to receive and act on results significantly. 

Rapid antigen test COVID-19

OVERVIEW OF DROPTECH COVID-19 RAPID ANTIGEN SWAB TEST METHOD

COVID-19 antigen throat swab test

COVID swab test using antigen tests give at-location results in less than 15 minutes and do not have to be processed in a remote laboratory. Yet that ease of use and rapid test speed comes with a cost in sensitivity. The rapid COVID swab test does not amplify the sample like PCR does. Whereas a typical PCR test can detect a single molecule of ribonucleic acid (RNA) in a sample, antigen tests need a sample to contain larger amounts of viral load to produce a positive result. So, if a person has low amounts of virus in their body, the test might give a false-negative result. 

For meaningful test results, a number of factors have to be taken into consideration. At the time of testing, variable factors like viral load, days since onset of symptoms, sample collection method, concurrent medication, ambient test environment setting, swab processing technique as well as the product quality and number of tests sampled all play an important factor.

Droptech COVID swab test

When performed correctly on people who were positive for SARS-CoV-2 confirmed by standard PCR test and within a week of the onset of symptoms,  the DropTech Rapid Antigen Detection Test showed a sensitivity of over 92% and specificity of over 97%; this represents an accuracy significantly higher than that recommended by the World Health Organization (WHO).

In white papers updated in October 2020, WHO suggests that testing people with rapid antigen test twice a week with a relatively less sensitive test could be more effective at curbing the spread of SARS-CoV-2 than more-accurate tests done once every two weeks using laboratory based PCR methods.

Even when COVID-19 swab test results are negative, people should continue to wash their hands, wear masks, and avoid gathering in big groups. Testing cannot replace the basic control measures that need to be in place to keep COVID-19 under control. People with symptoms of COVID-19 (cough, fever, shortness of breath, loss of taste) should self-isolate regardless of a negative test.

SARS-CoV-2 Viral Load

A typical antigen test starts with a healthcare professional or trained individual swabbing the back of a person’s nose or throat. The swab is made with special specimen-collecting resin which needs to come into contact with respiratory passage mucosa. Coronavirus multiply in high numbers at the area of the tonsils and back of the nose. Due care needs to be taken to avoid touching the mouth or tongue as saliva enzymes interfere with the test’s accuracy.

Coronavirus Incubation Period

Viruses multiply rapidly in affected non-immune individuals. At this stage, the person is a carrier with no symptoms. The number of viruses grows exponentially as time passes, in fact hour-by-hour. An infected patient may have an undetectable viral load initially, which becomes readily measurable at subsequent tests. The incubation period of the coronavirus SAS-CoV-2 is 5 to 10 days.

Time from exposure to the coronavirus

The coronavirus levels become detectable within 24 hours of transmission and before a person shows any symptoms. Once infected, the number of viral material grows rapidly and is usually detectable after 24 hours.

COVID Antigen Swab Test Sampling Method

A typical SARS-CoV-2 antigen test starts with a healthcare professional or trained individual swabbing the back of a person’s nose or throat. The swab is made with special specimen-collecting resin which needs to come into contact with respiratory passage mucosa. Coronavirus multiply in high numbers at the area of the tonsils and back of the nose. Due care needs to be taken to avoid touching the mouth or tongue as saliva enzymes interfere with the test’s accuracy.

COVID-19 Test Handling

Once obtained, the sample is then mixed with the supplied reagent solution specific to this test. The reagent breaks the virus open and frees signature viral proteins. Using the measured pipette, three drops of the mix are then added to the receiving well on a pregnancy-test-like cassette. The well feeds into a paper strip that contains an antibody tailored to bind to these proteins. If they are present in the solution in high enough numbers, a positive test result can be detected as a dark-coloured band on the white paper background. A red line appears as control indicating that the test is valid.

COVID Swab Testing environment

Tests perform best at an ambient temperature of between 3-30℃. Mouth wash, disinfectants or gargling with water in the previous hour to collecting the sample may lead to reduction in the number of detectable virus antigen in the sample.

Processing technique

Swab samples are immersed in the supplied reagent bottle for a chemical reaction that takes at least one minute to complete. Care must be taken to observe the time of this reaction and not to remove the swab prematurely. The DropTech COVID swab test uses a lateral flow technique. It takes 10 minutes for the solution to travel from the dropping well on one end of the cassette to the test area. Tests should be read once the red control strip is visible. Any results read after 15 minutes are invalid and should not be considered.

Past Infection

It is well documented that viral load peaks early in SARS-CoV-2 infections and then gradually declines, with tiny amounts of virus RNA staying in someone’s nose or throat for weeks or possibly months. And although there is not enough data to equate different viral levels with how infectious people are, there is evidence that individuals are unlikely to spread the virus beyond eight to ten days after showing symptoms. This supports the clinical utility of accurate rapid COVID-19 test kits.  A false negative result may be due to a person not having enough viral antigen, but in these individuals they may no longer be infectious and a risk to close contacts. When infectiousness is high, earlier in the course of disease, the rapid antigen test is more likely to yield a positive result in infected individuals.