I wondered the same thing. Not only are they sharing air with contagious people in poorly ventilated areas, but their own viral load isn't shed like it is outdo

I wondered the same thing. Not only are they sharing air with contagious people in poorly ventilated areas, but their own viral load isn't shed like it is outdoors. I also wonder about outdoor activity and mucus generation. Pollen, dirt, etc all trigger mucus generation and expectoration (coughing it out). External loads are caught up in this mucus and coughed out before you can get sufficiently infected and our own viral load can get caught up in the same mucus and coughed out as well. I have no experience in this field, just random thoughts. I'd love to hear from others with more experience in the field.