Because influenza is a respiratory infection.
This is one of my pet peeves. Make a note of it.
I wouldn’t care but the flu is one of those things I’ve chosen to highlight as an area of extreme interest*. I just like plagues, viruses, bacterial infections, epidemics. I had never heard about the Flu of 1918 until a few years ago. I found it shocking that I had never heard of something that had killed so many people so I looked into it. Fascinating somehow. That lead to bubonic plague reading (where I learned interesting facts about the origination of property law in the 1400s) and episodes of plague in the New World, like post quake SF. There is just something about how these things enter the body and do their work that gets me hooked. Too bad I don’t have the motivation or (how do you say “give a shittitude” fortitude? yah that might be it) fortitude it would take to become some kind of bio researcher. Yeh, instead I languish away in an office with my double major in acting and dance. Awesome.
* Along with volcanoes and brain evolution and whole grains and whatever else I decide fits.