If you've had COVID-19, it is possible that you could continue to test positive on a PCR test for months to come.

"How a PCR test works is that it detects genetic traces of the virus in the sample," explains cardiologist and epidemiologist Dr. Christopher Labos. "Somebody that has very, very small traces of genetic material still in their system after a COVID-19 infection could in theory test positive long after the infection is gone and they're not infectious anymore."

It's a rare occurrence, Labos notes, but it could prevent someone from participating in activities that require a negative test.

For example, most airlines require a negative COVID-19 test to board a plane.

"Some countries require you to test negative before you arrive. Some places require you to test negative when you get on the plane. Some places have no testing requirements," Labos points out. "It's not for the airlines to start doing medical triage. That's beyond the scope of their mandate. So, this is a situation where you would actually be in a bit of a pickle because you would have a positive PCR result."

He estimates someone could get COVID-19, recover completely, not be infectious and still test positive for days, weeks or even months after the fact.

"We don't actually know how common it is because most people don't get tested after an infection," he states. "There haven't been that many documented cases, but it does happen. It's not unexpected. So we have to be mindful of the fact that this is a possibility."

Nevertheless, Labos notes if it's been at least two weeks since symptoms first appeared, chances are a person is no longer contagious.

"I think it underscores the point that you need to treat the patient, not the lab results," he said.

And as with most rules, there can be exceptions.

To enter Canada, a traveller who previously tested positive for COVID-19 and is now symptom-free will be allowed into the country as long as they provide proof of a positive COVID-19 test taken "at least 11 and no more than 180 days before the initial scheduled departure time of your aircraft or your scheduled entry into Canada by water or land."

According to the government of Canada, the proof of positive result must be from an accepted type of molecular test.

These include:

  • PCR - Polymerase chain reaction;
  • Nucleic acid test (NAT) or Nucleic acid amplification test (NAATs);
  • Reverse transcription loop-mediated isothermal amplification (RT-LAMP);
  • RT-PCR – reverse transcription real-time PCR;
  • Quantitative PCR (qPCR);
  • Isothermal amplification;
  • Droplet digital PCR or digital droplet PCR (ddPCR);
  • Transcription-mediated amplification (TMA);
  • RNA (Ribonucleic acid);
  • Ct (cycle threshold);
  • CRISPR;
  • Sequencing;
  • Next generational sequencing (NGS) or whole-genome sequencing (WGS);
  • Oxford Nanopore sequencing (LamPORE);
  • Detection of the N gene;
  • Detection of Orf1a/b;
  • Detection of the S gene;
  • Detection of the E gene;
  • Detection of the RdRp gene.

Anyone looking to travel can now book a test on Clic Santé by selecting "COVID-19 Screening - without symptoms."

"This service is for individuals who are symptom-free for COVID-19 and who wish to be tested for the purpose of obtaining a certificate for travel," the portal notes. "This appointment is for a private screening service offered in a pharmacy and a fee will be charged on site."

Rapid antigen tests are not an accepted type of test to prove negative or positive status.

A positive test result within 72 hours of planned entry into Canada is also not considered valid and in this case, the government states a person will be denied.

The rules do change country by country -- and even airline to airline -- so travellers are encouraged to research entry requirements for each place they are visiting in advance of showing up at the airport.