Back when I was working in Illinois, I got the flu every year. Along with countless colds. It came from work. I worked with a bunch of overtime hungry workaholics. They would NEVER take a day off if they were sick. The just worked sick, and spread it to everybody. And during the Winter months there were at least a half dozen of them walking around the shop snotting, sniffling, coughing, and sneezing. Plus they were all grabbing the machine handles spreading their germs everywhere. It was impossible not to get it.
I would usually start getting the chills after lunch. And by quitting time I was sick as a dog, with water pouring out of my nostrils. I would usually end up missing a couple days from work, and felt like crap for a week or more.... After we moved to Arizona it all stopped. If it was the dry air, or the warm weather, I don't know. But when I was working for McCulloch Corp. here in Lake Havasu, they had a full time nurse working there. If she, (or anyone else) saw you walking around sick, you would get sent to see her. If she deemed you were coming down with something, you got sent home. Like it or not. And when you felt better, you had to check in with her before clocking in. If you had any type of fever or redness in your throat, you got sent home again. They didn't want the whole joint infected. I don't blame them.
Now that I'm retired out here, I've been in good health ever since. Not so much as a sniffle. Covid and all.... Knock on wood. I'm no doctor, but personally I think it's the cold weather back there. The buildings are all closed up tight, packed with people, all Winter long. All with the heat running 24/7. It's like working in a giant incubator.