Health care professionals outside the Viral Area being used to test for possible COVID-19 cases at the San Fernando General Hospital.

Paul Crooks DVM

COVID-19 continues to be the major news story around the globe and we still have many months to endure before life returns to its pre-coronavirus state. While we wait, testing will remain the bedrock for control of disease spread.

So let’s address the testing myth. The one which says: “My test results negative. Dat means I doh have d‘rona! Time to fete.”

Not so fast good reader. There are a few types of tests in circulation and interpretation of results varies widely.

The least accurate type of test right now is the SARS-CoV-2 Rapid Antigen Test.

Regular readers will remember that an antigen is an immune stimulant – often a protein produced by a micro-organism in the case of infectious disease.

Antigens provoke the immune system to produce specific antibodies, which at sufficient levels prevent disease – thereby conferring immunity.

Rapid antigen tests are meant to determine active or current infections in a few minutes. However, because the accurate diagnosis of infected persons is necessary for control of COVID-19, the far more accurate Polymerase Chain Reaction (PCR) tests – done by the Ministry of Health – should be the only one employed for this purpose.

This test works by amplifying then detecting DeoxyriboNucleic Acid (DNA) present in micro-organisms. Members of the coronavirus family have only RiboNucleic Acid (RNA), but advancements in technology mean that presents no barrier to PCR diagnosis. Although quite expensive and relatively slow – with delays of sometimes greater than 24 hours for results – if one were to test negative on PCR, it is highly unlikely that that person is infected. PCR is the best test for the detection of active cases and everyone showing clinical signs should undergo a PCR test.

The last broad group of tests is Rapid Antibody Tests. These are generally quite accurate and give results in a few minutes, but should not be used to confirm active infections since early infections may be missed.

Additionally, while SARS-CoV-2 remains a threat, persons with detectable antibodies should be subjected to a confirmatory PCR.

This type of test would be best utilised for large-scale, cost-effective screening of higher-risk groups including healthcare professionals, and those classified as essential employees in all sectors. Rapid antibody tests are probably going to detect the majority of asymptomatic or subclinical cases. Readers should be aware that the presence of antibodies does not necessarily equate to immunity.

Ultimately, the wider the testing, the more likely that all cases are captured, providing more accurate data for making informed decisions. Remember that negative results do not mean that you are disease-free. Therefore, regardless of status, adhere to social distancing guidelines.

If you think you have COVID-19, do not go to a laboratory or doctor, but call the Ministry of Health’s hotline at 877-WELL (9355). The results of any medical tests should be discussed with your physician.

In the meanwhile, for more information on this or any other health topic related to your pet, farm, or wild animal, please call us (868) 239-7837.

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