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As a physician and infectious disease epidemiologist, I’ve seen a lot of COVID-19 patients during the pandemic, and there’s a question I hear over and over:
How is it possible that my partner — or child or sibling or roommate — tested positive for COVID-19, and even though I slept in the same room or lived in the same house, I didn’t come down with the virus?
Weren’t they breathing out infectious particles for days on end? And I assume I was breathing them in.
There is an answer to this question. But it’s a bit complicated.
First, let’s review how SARS-CoV-2, the virus that causes COVID-19, spreads. While some viruses are primarily passed through contact with the bodily fluids (Ebola) or skin (mpox) of someone who’s infected, SARS-CoV-2 is easier to catch. It’s spread mainly through the air in invisible aerosols (and to a lesser extent in large droplets) that the infected person emits while breathing, talking, sneezing, coughing, laughing or snoring. The aerosols can hang around in the air for hours, and others can inhale them.
So yes, if someone in your house is exhaling SARS-CoV-2-viral particles, you could breathe them in and become infected. But … here’s why that does not always happen.
There are two points to ponder. One: The person with COVID is not contagious at all times. Two: Different factors can reduce the risk of getting infected by a housemate.