Inconsistent Covid-19 tests cause panic

Many Pretoria residents are worried about just how accurate Covid-19 test results might be after receiving apparently “inconsistent” test results.

Michelle de Jager, a mother from Zwavelpoort, recently shared her experiences in this regard with Rekord.

Her four-year-old son has immune defects, which meant he struggles to fight any bacteria or disease.

“If there is anything in the air, then he is the one to get it,” said De Jager.

“So for him Covid-19 would be extremely dangerous.”

The boy was scheduled for a bronchoscopy and drainage of fluid from one lung and, according to procedure, he and his mother were both tested for Covid-19.

Michelle said her son’s results came back negative and he was thus sent to theatre.

“They, however, wouldn’t allow me to accompany him because my results weren’t back yet,” she said.

“While I was waiting, I got an SMS stating that I was positive. I was shocked.”

She said the hospital then declined to perform her son’s operation due to her testing positive even though the boy was negative.

“It just didn’t make any sense. My son and I were sharing everything, we were sharing a bed at hospital.”

They were, however, sent back home and had to remain in isolation.

Two days later, she received results of tests she did at a different lab. These tests came back negative.


Irene le Grange

“My husband and I tested positive and later negative within a matter of only a few days,” local resident Irene le Grange also told Rekord.

Le Grange is the mother to a six-month-old baby, a home cardiac patient who was supposed to go for a check-up at a hospital in May.

As a precautionary measure, both Le Grange and her husband got tested for the coronavirus two days before their baby’s admission.

“The following day, my husband got an SMS from the lab saying he was negative,” she said.

A medical local expert believes there is an explanation.

According to clinical pharmacologist and medical practitioner at Intercare Woodhill, Dr Morné Strydom, the most commonly used test for Covid-19 diagnosis was the RT-PCR test.

“This test is highly sensitive and specific towards genetic markers of the virus,” Strydom said.

Samples for testing are done by collecting nasopharyngeal or oropharyngeal swabs or from other respiratory tract secretion sources like sputum.

Strydom said, with the RT-PCR test, labs could only test a swab sample submitted for testing.

“The lab could only confirm whether specific virus was detected or not detected from the specimen submitted.

“Depending on the quality of the swab taken and other factors, it is possible to have the virus, but test negative on a swab,” he said.

“Your post-nasal drip secretions at the back of your throat will fluctuate during the day. The patient may be congested with blocked sinuses. At a different time of the day, there might be more free-flowing sinus drainage, which may host more viral particles.

“We may take a swab at a time of the day when you do not shed a lot of virus in your secretions. So you could be swabbing at the back of the throat or nose, but not ‘catch’ any viral material on the swab for it was not present in detectable concentrations in those secretions at that moment.”

Swabs could be taken from people shortly after having gargled, flushing their noses with nose sprays, drinking hot beverages, chewing bubblegum, sucking on throat lozenges, etc.

All of this minimises the chance of “catching” the virus – despite a good quality swab technique used by the healthcare worker.

“For example, you’ve had a nice warm cup of coffee and ‘burnt’ your throat clean. Now Lab A takes a swab in the back of the throat by collecting an oropharyngeal swab. Chances are it will come back as ‘not detected’ or ‘negative’.

“Now Lab B may use and different technique to collect the sample. Hence, the test may have a higher probability of detecting the virus, resulting into a positive test result.

Dr Strydom said the RT-PCR test was highly sensitive for the SARS-CoV-2 virus.

The chance for “false positives” are thus very unlikely, unless the sample was contaminated.

“If I take a swab from a truly infected person and was ‘lucky enough’ to get a good quality swab by collecting sufficient amounts of virus material in detectable levels at that point in time, the patient will most probably test positive,” he said.

“If you test negative with a follow-up test a day after or even on the same day, that does not invalidate the positive test.

“If you’ve tested positive, you are positive.”

He therefore advised people who tested positive to self-isolate and not waste money and resources on repeated “confirmatory tests”.


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Read original story on rekordeast.co.za

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