What you need to know if you’re getting tested for Covid-19 before seeing family

If you’re getting tested for Covid-19 before gathering with family and friends during the holidays season, even if your result was negative, you may not actually be in the clear.

Given that a negative Covid-19 test has become a ticket to skipping quarantine when traveling across many state lines, it is easy to believe that a negative test means you are risk-free of carrying the virus.

But the reality is much more complicated. A negative test does not mean you do not carry the virus, rather it means you did not have the virus during a specific snapshot of time, experts say. Covid-19 tests are not sensitive enough to pick up traces of the virus the day after someone is infected, and sometimes, it can take more than a week for a test to detect the virus after infection.

Amanda Simanek, an associate professor of epidemiology at the University of Wisconsin–Milwaukee and a member of Dear Pandemic, a social media public health campaign run by a cohort of female public health and economic experts, spoke to the Guardian about the main things people should know when relying on testing as a strategy to prevent the spread of Covid-19.

Related: US surpasses 13m Covid cases as experts urge caution over Thanksgiving weekend

You may be getting tested too early

Covid-19 has an incubation period of between two to 14 days. About half of people who contract Covid-19 will develop symptoms within five days of exposure. But for some people, it could take up to two weeks.

“If up until the day you got tested, or even a few days before you got tested, you’re just going about your life as normal and not taking other precautions to prevent exposure to Covid-19, that negative test is really telling you you don’t have a detectable virus on that day,” Simanek said.

“You could be exposed, get tested on day two or three after that exposure, be negative, and then on day eight develop symptoms.”

Simanek cited fellow public health expert Megan Ranney, an emergency room physician and researcher based in Rhode Island, who compared the sensitivity of a Covid-19 to that of a pregnancy test. “Just like a pregnancy test cannot take the place of birth control, Covid-19 tests should not be seen as a substitute for robust strategies to reduce community transmission,” Ranney wrote in an opinion for NBC News.

That does not mean you should avoid getting tested, but means that testing alone cannot guarantee you will not transmit the virus. A Covid-19 test taken after five days of quarantining is much more informative about whether you have the virus than one taken without quarantining. “Then you know there’s a certain date at which a last known exposure could have occurred,” Simanek said.

How you quarantine matters

If you want your Covid-19 test to be useful, you have to take your quarantine seriously.

It means you should be avoiding the grocery store and opting to get your groceries delivered. Parents of children who are going to school while quarantining are technically not quarantining. You, or anyone in your household, should not be interacting with anyone outside your household in-person. “It doesn’t mean running errands but avoiding everything else,” Simanek said.

If you are traveling, it means you should not be making contact with people en route to your destination. Airplanes, buses and trains are no exception.

“You should be isolating yourself from others, just do what you can to rule out any exposure.”

Simanek acknowledges that there are logistical challenges to carrying out such a strict quarantine. “That’s challenging for families that aren’t able to work from home or whose kids are in in-person school or are going to childcare because they themselves are an essential worker.”

But this type of quarantine is the best way to ensure that a negative test is not false.

Testing is most informative on a larger – rather than individual – scale

Covid-19 tests are most useful for community-level action and monitoring the spread of the virus on a wide scale.

A handful of states have allowed travelers to bypass a mandated quarantine period for people who have tested negative for the virus, usually no more than 72 hours before their arrival. While that can be helpful to public officials trying to mitigate the spread on a broader scale, the same strategy is not so useful on an individual level.

“Testing is a vital component to the broader strategy to contain Covid-19 in your community,” Simanek said. But for people who want to visit family, a negative test “is not particularly informative and doesn’t necessarily change the course of action you should take”.

“If you’re talking about visiting your grandparents, you don’t know if you’re that 50% [of people] who get symptoms by day five. Getting a negative test and assuming you’re in the clear, that’s a risk that you’re going to transmit to your family members. That’s a risk I wouldn’t take, personally.”

Bottom line: Tested negative? You still should be practicing other safety measures

This does not mean you should cancel all holiday plans, but underscores the need for additional safety precautions if seeing at-risk family and friends, even if you get a negative test and especially if you have not been properly quarantining amid potential exposure.

As guidelines from the Centers for Disease Control and Prevention (CDC) say, an outdoor celebration is much safer than indoors, where the virus is most likely to spread. Masks and social distancing are essential. When eating, try to stay far apart and use separate utensils.

Or have a virtual gathering, a guaranteed risk-free way to celebrate the holidays.

“The nature of this virus is such that you can have it and you don’t know it yet, you don’t have symptoms, [but] you can pass it to other people,” Simanek said. “It behooves us all to basically assume we have been exposed and act accordingly.”