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How accurate are the COVID-19 swab tests?

DETROIT – One of the most important elements to reopening is increased testing for COVID-19, yet many residents still have questions and concerns about testing issues.

Before we move forward, we should define testing to make sure everything is clear. Right now, we’re talking about swab testing the back of the nose to find virus particles that are being shed by someone with an active infection. Blood testing for antibodies -- which provides evidence of a prior infection -- isn’t ready for widespread use, but swab testing also has challenges.

Swabbing the back of the nose to collect a sample sounds simple enough. The first thing you need is a swab, but for the test to work, the swabs have to be specially made. They cannot contain cotton, wood or any organic components. Because of this, there is a shortage of supply of these swabs and the supply has not met the demand.

For the test to be valid, a good sample needs to be collected and the lab or machine it’s processed in also needs to be accurate.

An issue many people have identified is that the swab tests can only tell if a person is shedding virus at the time it’s done. For example, if a swab is done in the incubation window -- after a person is exposed, but before the infection has developed -- the test can come back negative, but the person will become infected.

This doesn’t mean testing is pointless though. Knowing who might be an asymptomatic or presymptomatic spreader is critical, and certainly knowing if someone is positive is essential, but it’s just as important to understand the limitation of the test. It is only sampling a single point in time, which is also why -- even with widespread testing -- the use of masks, hand washing, and social distancing will not go away.


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