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Katherine J. Wu, Ph.D.

23 Dec, 6 tweets, 2 min read

Tests don't stop when you get your result. Think about the circumstances under which you took that test — they could really influence how you interpret what that test tells you. 1/

nytimes.com/2020/12/23/ups…

For starters: Positive and negative can be useful words, but we should be careful not to overinterpret them. Think instead about "detected" and "not detected." We're describing what a test has found — not a permanent identifier that says anything about who you are as a person. 2/

A "negative" result could be outdated within hours, either because the virus has built up to detectable levels, or because you were exposed anew.

"Positive" in the context of disease can also sound incriminating. 3/

Another crucial concept? Pretest probability - basically, the confluence of factors that raises your risk of having the virus in the first place. Do you feel sick? Were you recently exposed? Is there a lot of virus in your community? That affects interpretation. 4/

These are the questions testing experts ask. Now that many tests are being used outside of health care settings, we're having to learn to interpret results on our own, and recognize that they're not as binary as they seem. 5/

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Katherine J. Wu, Ph.D.

@KatherineJWu

3 Dec

Hundreds of millions of coronavirus tests have been run in labs across the country since the pandemic first hit.

Behind every single one of those tests is a team of people. I wrote about a few of them, and the herculean efforts they've put in. 1/

nytimes.com/2020/12/03/hea…

The world has never asked this much of clin micro and public health lab workers.

Tests are not just pushed buttons and sloshing liquids. They make fingers ache. They make eyes water. They require sprinting back and forth, and perfect pipetting precision. 2/

We do not often look inside these labs. And for decades, that's been okay. “We’re accustomed to holding things up in the background," one scientist told me. "We enjoy doing it because we know we’re helping people.” 3/

Read 10 tweets

Katherine J. Wu, Ph.D.

@KatherineJWu

22 Nov

In the leadup to the holidays, maybe we can start talking about our coronavirus tests in a slightly different way.

If you do not test positive for the coronavirus, consider that is more about the virus being "not detected," rather than you being "negative" for the virus. 1/

Because maybe the virus is there — but it's not yet present at high enough levels to be found on a test. You could still be infected. You could still be contagious. You could test again tomorrow and be positive; you could test again in five hours and be positive. 2/

Or perhaps you're not infected yet. A test is a snapshot in time; it says nothing about your status in the future. Every trip to the grocery store, even masked, could be an exposure. And a test today won't catch tomorrow's infection. Tests are also imperfect. 3/

Read 5 tweets

Katherine J. Wu, Ph.D.

@KatherineJWu

12 Nov

A few weeks ago, I heard scattered rumors about bizarre positives coming out of coronavirus testing programs at universities.

It didn't seem to be the coronavirus. It also wasn't contamination in the labs processing the tests. It was weirder. 1/

nytimes.com/2020/11/12/hea…

Researchers working with harmless, noninfectious genetic material from the virus (in the form of DNA) were testing positive, over and over again.

They weren't shoving their science up their noses. They were being careful, and doing great work.

The DNA clung to them anyway. 2/

If that DNA happened to overlap with the target of a coronavirus test, that quickly spelled trouble for some. The test picked up that "contaminating" DNA, and thought hey, this is exactly what I was looking for. Positive. 3/

Read 22 tweets

Katherine J. Wu, Ph.D.

@KatherineJWu

2 Nov

Rapid tests are already being used to screen people without symptoms for the coronavirus — even though they're not cleared for this purpose, and the data in asymptomatics is sparse.

Some of that data is emerging. It might not be what some hoped. 1/

nytimes.com/2020/11/02/hea…

Is there still a role for rapid tests? Absolutely. More data will be needed to figure out where they fit in best. But for now, it's crucial for people to understand that not all coronavirus test negatives are created equal. 2/

Testing negative on less sensitive tests, for example, might not mean you're virus-free.

Could it mean you're not infectious? Maybe. That's really, really hard to test.

It's very likely to be the case that people will less virus in their bodies are less infectious. 3/

Read 10 tweets

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