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‘Not Detected’ in COVID terms

‘Not Detected’ in COVID terms

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Let me tell you a cautionary tale. A couple of weeks ago, I was covering the Dominion Energy Charity Classic when I felt what I thought was an old friend coming on: allergies. My nose was getting itchy. Drainage was irritating my throat.

But it didn’t feel like a big deal and I wasn’t worried. I was wearing a mask, keeping my distance, and being careful about not touching anything more than I absolutely needed.

Overnight, while I was trying to prepare the forthcoming sports sections for the week’s Locals (Mechanicsville and Ashland-Hanover), it started to feel like more than mere allergies. I was stuffy, sneezing and coughing.

By Monday morning, all I wanted to do was slap my sections together and go back to bed. By Monday night, I was running a fever.

By Tuesday morning, I had met enough criteria for COVID-19 that I went to my doctor to get tested. Because of the usual trajectory my body typically takes with any kind of respiratory infection, she also began treating me for bronchitis.

I spent the ensuing two weeks in isolation. I got tired of being stuck at home. But that is irrelevant. I’m not writing all this to kvetch to you readers. I’m writing because there’s an important lesson to be learned.

When the nurse called me to give my result, she said it was “negative.” I used the term “negative” myself in describing the result. Most people, after getting a similar result, would likewise use “negative” to describe their COVID status.

Here’s where the cautionary bit comes in: The lab report does not say my result is “Negative.”

Instead, it says, “Not Detected.”

You may be guessing the punch line at this point. … Yes, there is a difference between “Negative” and “Not Detected.”

In my years as an environmental regulator reviewing toxic substance monitoring reports, I never saw a report that said a chemical was not present. If the substance was detected, there would be a number representing the concentration of the pollutant in the sample. If the sample was not detected, there would be some notation like “DL” that was shorthand for “below detection limit.”

Most biological or chemical assays are only so sensitive in that there must be a minimal amount of whatever of interest for the test to register. That is referred to as the detection limit. At or above that minimal amount, the test can quantify how much is there.

But, if the amount of the thing of interest is below the detection limit, you cannot do the opposite and conclude it is not in the sample. It might very well be in sample, but in an amount too small for the test to be able to measure.

We run into this dilemma with the COVID-19 tests. If the results say the virus has been detected in your sample, odds are you are infected. The tests have not had a big problem with false positives – except where, as with the initially rolled out version of the Centers for Disease Control and Prevention test, the test kits (or samples) are contaminated in some way.

If you have no COVID symptoms and your sample comes back “Not Detected,” it may be reasonable to conclude that you are not infected. Nevertheless, you could be mistaken. If you’ve had a recent close contact, you still need to be careful.

Testing of my sample was done via LabCorp. The results of my sample came back “Not Detected,” but that’s where the detection limit comes into play. I could still be COVID-positive, yet shedding virus at levels too low to register.

According to LabCorp’s emergency use authorization documentation, the viral test – which looks for copies of viral genetic material, not the antibodies we may (or may not) produce against the virus – has a detection limit of 6,250 copies per milliliter.

Other tests have been developed that can detect far lower concentrations of virus, but some can only detect higher concentrations. As with everything, cost/benefit considerations apply, and the LabCorp test is intended for a mass, not a niche, market.

“The LabCorp test is likely sufficiently sensitive to identify patients who are ‘infectious’ on the day of testing assuming the sample was collected appropriately,” wrote Harvard University researcher James E. Kirby via email (response slightly edited for clarity). “It is one point in time. Detected viral load usually precedes symptoms; however, I don’t know if this is always the case. And if you test patients later during infection viral load starts to fall and becomes undetectable, at this point you may still be infected, but not infectious.”

In my case, let’s say there were 6,000 copies per milliliter of virus in my sample. I would definitely be COVID-positive, but my test result will be just as “Not Detected” as if I had zero copies per milliliter in my sample.

So, if you find yourself in that situation, what should you do?

Here’s what the LabCorp emergency-use authorization documentation says:

“Negative results do not preclude SARS-CoV-2 infection and should not be used as the sole basis for patient management decisions. Negative results must be combined with clinical observations, patient history, and epidemiological information.”

Emily Goldberg, a spokesman for LabCorp, put it this way:

“A positive result is considered definitive evidence of infection with COVID-19. However, a result of negative does not definitively rule out infection with COVID-19.”

In other words, if you’ve been exposed, or even worse, have symptoms – BE CAREFUL!

I possibly had a recent close contact – kind of a two degrees of Kevin Bacon thing that I initially overlooked.

Likewise, I had symptoms (and still do as I write this). I had some symptoms typically found with a cold, but not the flu.

I had some symptoms typically found with the flu, but not a cold. All of the symptoms are common with COVID-19. I also had some weird ones that have been reported in folks with COVID like foul-smelling urine. (I have that asparagus thing, so I can recognize when something is “off.”)

In my case, the smart play is to assume I am positive and do all the things I’m supposed to do to avoid spreading COVID to others: isolate, wear a mask when I can’t, wash my hands, cover up my coughs, be careful about touching my face and surfaces around the house, etc. I’ve been trying to be a good boy. I’m not perfect, but the effort is there.

I would prefer to see more of our fellow residents taking this more seriously. Instead, I see far too many people refusing to wear masks, not respecting other folks’ social distance, and – at least the last time I was in a public restroom – refusing to wash their hands. (Guys, grow up!) I hear a lot of folks shouting “Freedom!” and “Rights!” but few discussing “responsibility.” But it’s long past time to be responsible. Lives – including mine – depend on it.

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