I tested negative. Am I safe?

More folks than ever are getting tested for SARS-CoV-2, the virus that causes COVID-19. Access to testing is great, and long overdue.

But the tests themselves remain problematically inaccurate, so remember that a negative test doesn’t necessarily put you in the clear.

The issue is false negatives: tests that don’t detect the virus when a person is actually infected. And these tests we’re using to determine viral presence is prone to false negatives.

This matters because people who test negative may take fewer precautions to protect those around them — even though they may actually be infectious.

If you’re sick, pay attention to your experience rather than your test results — and act accordingly. But if you’re not sick, don’t take the test’s word for it.

How bad is the problem? Researchers at Johns Hopkins School of Public Health scoured the existing scientific literature — both published, peer-reviewed studies and those that are still going through the process — to answer that question. They looked at data for the RT-PCR test, generally a very sensitive way to detect viruses, that is the primary swab-up-the-nose test used to detect active infection.

The short version: At best, one in five tests will have false negatives.

Published in the May 13, 2020 edition of Annals of Internal Medicine, the study found a sweet spot in the progression of infection. Testing on Day 8 of the infection — usually the third day of disease symptoms — is when you’re most likely to get the most reliable results.

Here’s how it breaks down:

  • Day 1 of infection (often no symptoms): 100-percent chance of a false-negative test.
  • Day 4 of infection (often no symptoms): 67-percent chance of a false-negative test.
  • Day 5 of infection/symptom onset: 38-percent chance of a false-negative test.
  • Day 8 (three days after symptom onset): 20-percent chance of a false-negative test.
  • Day 9 (4 days after symptom onset): 21-percent chance of a false-negative test.
  • Day 21: 66-percent chance of false-negative test.

These numbers represent median observations: in half the cases the chances were higher, in half they were lower. This is the middle ground of numbers that have a pretty large spread, especially when testing the early days of infection.

Going with these median numbers, you’ll see that even at the Day 8 sweet spot, one in five tests will falsely report a negative result when the person is actually positive. So at best there’s a 20% false negative rate. On other days, the false negative rate is even higher.

Why are the false negatives so high on a test that is known to be exquisitely sensitive? A physician colleague of mine working in a front-line lab suggests that incorrect or incomplete collection may be the problem. The swabs healthcare workers stick up patients’ noses may just not be catching enough viral particles. I’ve got a message out to a microbiologist friend for his take, and will update this post when I hear back.

I get that people want to know what’s going on. I want to know what’s going on. These acute tests (the swab-up-the-nose tests) more usefully inform our actions when they’re positive than when they’re negative.

If you get a positive test, talk to your doctor about appropriate medical care, stay home, stay away from people, and do everything you can to take care of yourself.

If you get a negative test, don’t assume you aren’t sick or that you can’t infect others. If you aren’t on your third day of symptoms (and even if you are), there’s a good chance the test won’t catch your infection.

Be careful, folks. And remember that getting a negative test isn’t the final word.


—Dr. Orna

P.S. Read the full Annals of Internal Medicine article, “Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction–Based SARS-CoV-2 Tests by Time Since Exposure.” Here are the key findings if you don’t want to wade through it:

“Over the 4 days of infection before the typical time of symptom onset (day 5), the probability of a false-negative result in an infected person decreases from 100% (95% CI, 100% to 100%) on day 1 to 67% (CI, 27% to 94%) on day 4. On the day of symptom onset, the median false-negative rate was 38% (CI, 18% to 65%). This decreased to 20% (CI, 12% to 30%) on day 8 (3 days after symptom onset) then began to increase again, from 21% (CI, 13% to 31%) on day 9 to 66% (CI, 54% to 77%) on day 21.”

Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction–Based SARS-CoV-2 Tests by Time Since Exposure.Annals of Internal Medicine, 13 May 2020.

Photo by Hans Reniers on Unsplash

exercise: the best mood medicine (podcast)

Growing up, I was a kid who hid in the back corner during gym — because dodgeballs are hard and kids are mean. I never developed a sense of myself as athletic, and mostly didn’t miss it.

Instead, I found my physicality by carrying life essentials on my back for four days on a backpacking trail. It was life altering — but somewhat location dependent.

Several years ago, I hit a personal low. I had tried pretty much all the things, but wasn’t feeling any better. After being strongly advised by a non-medical friend to consider pharmaceutical medications, a Facebook post from a doctor friend jumped out at me: Weight-bearing improves mood.

So I tried it. And it made a huge difference.

Research and clinical experience have long supported exercise as a treatment for depression and anxiety. The side effects of exercise, properly applied, are increased strength, improved blood sugar balance, better immune function and more.

(Note that I don’t tout weight loss here. Not everyone loses weight, and not everyone needs to. Overall health should be the goal, with weight optimization a possible secondary side effect.)

When it comes to depression, research shows that while medications may work faster, exercise is equally effective after 16 weeks and better than drugs after 10 months. And it doesn’t take much: Just 20 minutes three times a week of moderate-intensity exercise makes a significant difference. (PMID: 15361924.)

The same pattern holds for anxiety. Even a single round of resistance exercise can lower anxiety significantly. (PMID: 25071694)

My patients will attest to this experience. Many of them start exercising and find the stressors that would stop their lives cold no longer affect them nearly as strongly. It’s been a lifesaver for them, as it has been for me.

I mention my story because it’s not unique: Many of us have traumas and resistance around athleticism, gyms and “exercise” in general. You don’t have to want to be an athlete to get these benefits. You just need to do the things.

I started going to the gym with the idea that it was something I had to do regardless of whether I found a strong community or even liked the activity. It was a prescription. In the end, it surprised me with both community and an activity I enjoy. I’m still no athlete, but having exercise as a tool in times of stress is a huge help.

The podcast below is one I did two years ago with Michael Skogg, the owner of Skogg Gym in Portland. (The gym is now virtual.) In it I review the science behind exercise as a treatment for depression and anxiety.

I hope you find the podcast both interesting and useful. If so, please share it with folks who could use the information and inspiration.


—Dr. Orna

P.S. Yes, that’s me in the middle of the photo. If you join Virtual Skogg you’ll see I’m a section header! They were very kind and let me use the picture here.

dr. orna recommends: spice apothecary by bevin clare

Food is medicine. You’ve heard me say that a lot.

This week I got a new book that takes the concept to the next level: Spice Apothecary by Bevin Clare.

Bevin is an herbalist, herbal educator and president of the American Herbalists Guild. She’s deeply committed to broadening the reach of herbal medicine and keeping it accessible to everyone.

What better way to do that than by leveraging what many folks already have in their kitchens? Better still, this helps people access medicine that makes food more delicious!

Spice Apothecary covers 19 commonly available kitchen medicines, including black pepper, cinnamon, lavender, mustard seed, thyme and turmeric. She includes health benefits, daily dosages and many recipes. (Parsley pistachio pesto!)

The book itself is physically beautiful, filled with gorgeous photographs and clear charts that simplify spicing up your life.

I’m calling this an inspiring addition to any herbalist or foodie’s bookcase. But keep it in or near the kitchen — you’ll want to use it.

Buy the book from the author here.
Buy the book online from Bookshop here.

—Dr. Orna 

Photo by Dan Gold on Unsplash