So, what’s behind the Samoan sailors confusing Covid 19 results
Someone else tested positive on one nostril and negative on the other recently which caused a bit of a stir online. Erykah Badu, the renowned singer posted her results on her social media accounts on 14th November, and later tested negative after a third test.
This is apparently not uncommon.
The recent announcement by the Government of Samoa regarding conflicting results of nasal swabs of a Samoan sailor who first tested positive, then negative for Covid 19 has received much attention on social media. His results from a laboratory in New Zealand showed one nostril tested positive and the other negative.
According to the US Food and Drug Administration, “positive results are usually highly accurate, but false positives can happen, especially in areas where very few people have the virus.” In the case of Samoa, where it is still Covid 19 free, this may very well be the case.
How the viral test works
The second test for the Samoan sailor was sent to Wellington, New Zealand according to the Government of Samoa for a second test to verify earlier results.
According to the New Zealand Ministry of Health website, the viral test looks for the virus itself. It does this by searching for the virus’ genes in a sample taken from the person being tested, usually a swab from the nose or throat. Genes are small sections of DNA — information carried inside the cells of all living organisms.
In technical terms the viral test is called a ‘PCR’ test. PCR stands for polymerase chain reaction, which is a laboratory method to make large numbers of copies from a very small sample of genetic material. So, the test can find really small amounts of virus genes in a sample.
A sample may also be collected from liquids from your lungs. The fluid is either coughed up or may need to be extracted. This method is not very common, and these samples are usually only taken when people are in hospital.
The sample is then sent to the laboratory and tested to see if it contains any genes from the SARS-CoV-2 virus — the virus that causes COVID-19. The result is usually available within 24 to 48 hours (depending on how quickly the sample can be transported to the testing laboratory and how many samples they have to process).
Why false positive?
The University of Cincinnati Health’s chief of Pathology and Laboratory Medicine Dani Zander, MD, says that the chance of a false COVID-19 test result depends on the type of test.
“A false-negative test can happen if one has a very low viral load,” Dr. Zander said in a press release by UC Health.
A viral load represents the amount of the virus in any given testing sample, like on a nasopharyngeal swab. Someone may have a very low viral load in the first couple of days after they’ve become infected. Their viral load may also be low at the end of the course of their infection, UC Health noted.
Other tests, such as a type of rapid test called an antigen test, are “less sensitive” to detecting the virus, Dr. Zander said.
False positives are also uncommon in PCR tests. It can happen in a situation where there’s cross-contamination, she said. “Laboratories work very hard to minimize the risk of cross-contamination, so it’s not common,” Dr. Zander said.
Should we take it as a positive?
According to MIT Medical, Covid 19 test almost never gives a false positive.
In a Covid 19 update, MIT Medical stated: “The test used to diagnose COVID-19 is a molecular test. This means that it works by detecting genetic material from SARS-CoV-2, the virus that causes COVID-19. When someone is infected, this genetic material can be found in the nose and upper throat. The test uses a sample that is collected by inserting a long swab into the back of the nasal passage through the nostril. The genetic material from SARS-CoV-2 cannot be confused with the genetic material from other viruses, so the COVID-19 test is highly specific. If you are tested for COVID-19, and the test comes back positive, you can be very sure that you are infected with this virus.”
But MIT Medical states that unfortunately, the test is not equally sensitive. If the specimen collection is not done perfectly, or if a patient is in an early stage of infection or already partially recovered from the illness, their nasal-swab sample might not contain enough viral material to come back positive
Contributing factors to mixed results
According to the FDA the handling of the testing kits could potentially lead to compromised results.
The issues include:
If the test components are not stored properly, this can affect the performance of the test.
The package insert for tests also includes instructions about reading the test results, including the appropriate time to read the results. Reading the test before or after the specified time could result in false positive or false negative results.
Processing multiple specimens in batch mode may make it more challenging to ensure the correct incubation time for each specimen.
Risks of cross-contamination when testing patient specimens, can cause false positive results. These issues include insufficient cleaning of the workspace, insufficient disinfection of the instrument, or inappropriate use of protective equipment (for example, failing to change gloves between patients) can increase the risk of cross-contamination between specimens with subsequent false positive results.
What’s next?
Health experts however warn that results should not determine preventative actions.
One Samoan medical professional said: “It is like everyone is waiting for a result to respond, when they can just prepare now and do the right things. We need to implement safety and prevention measures now.”
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