I’m sick now. I took my mask off for 5 seconds on an outdoor walk for a sip of water. An UNMASKED bicyclist rode right next to me. He was breathing quite heavily. Now I am sick. Not a coincidence. Covid is airborne.
The likelihood that you became ill from that particular encounter is near zero.
The average velocity of an amateur bicyclist on flat ground is roughly 7.6 meters per second. If we assume your bubble to 2 meters (according to initial social distancing guidelines), he was in your area for roughly a quarter second. There's a lower likelihood he was even sick given he was doing physical exercise. You were also outside (I presume) which is inherently low risk. As I said, it's not impossible, but the odds you got ill from that person specifically is near zero.
And yeah, masks do work really well, however, they aren't impermeable shields. I'm going to give you the benefit of the doubt and assume you were using an N95 mask, and if you were, the mask can filter at least 95% of particles at 0.3 microns. Covid is a 0.1-micron particle. Does that mean masks can't filter covid? No. Most viruses, like covid, are suspended in something, like water droplets, so the mask would filter through those viruses. The added benefit of masking is the reduction in breath travel distance. As a wearer, your breaths and coughs travel shorter distances, leading to a smaller exposure radius if you are infected. If you are healthy and wearing a mask. the air you're breathing is being drawn from a smaller area, so there is benefit there as well (however, it's greater if the sick person is actually wearing one).
There's a much higher chance that you got ill from 100 masked encounters rather than 1 unmasked encounter. However, if you had 5 masked encounters and 1 unmasked encounter in passing, more than likely, it was the unmasked encounter that got you sick. But I assume you interact with substantial numbers of people on any given day, even if you attempt to keep exposure to a minimum, so like truly, the chance this one guy got you sick is extraordinarily slim.
Only one in roughly 5000 Americans tested positive over the last two weeks (according to public testing data) and even if we assume it is a severe undercount (it almost certainly is) and say there are 10x or even 50x more cases, that's only 1 in 500 people or 1 in 100 people, so truly, the chance that one zooming past you for a mere moment got you sick, is extraordinarily low.
