Understanding a negative

In the historic COVID-19 pandemic of 2020, the disease has affected all aspects of life, including how volleyball is practiced and played. These posts are meant to be explanatory about the basics of coronavirus biology and public health, and seeing the big picture before applying it to learning volleyball.

The gold standard test for COVID-19 is the RT-PCR test, which detects the presence of viral RNA (the genetic material) from nasopharyngeal swabs (those are the long swabs that are stuck up the nose to sample the material). Additional technologies are being developed to detect the virus in less invasive material, such as saliva, and quicker turnaround chemistry, but those are not standard yet. The question that needs to be answered, from the perspective of the patient, “Am I infected and contagious?”, and the desired result is usually “No”.

But surveys show a pretty high false negative rate, as high as 1/3 of cases, where a patient is diagnosed as negative when in fact they’re positive. This is really concerning, of course, because a negative diagnosis is usually the assurance to participating in social activity with safety.

But why is there such a high rate of false negatives? Because proving the absence of something is extremely difficult with a test designed to find it. If you were looking for a object, say, your keys – how thoroughly would you search a room to assure yourself that they’re not there? If you did a quick pass and found the keys, you would be done (a positive result). But if you didn’t find them the first time, you wouldn’t be certain. In fact, interpreting a negative result is a matter of building confidence – multiple results in targeted period of time is what’s necessary, and even then, you’re never really sure if you hadn’t just looked under some corner of the room.

In the case of a virus test, the negative outcome is desirable – there’s incentive to not sample appropriately, or overlook test failure. So, getting a negative result doesn’t exempt a patient from appropriate infection control behavior. After all, a coronavirus negative person is potentially a positive one later on.

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