How are respiratory illnesses primarily spread?

They are mostly to spread through contact such as shaking hands. You can also get a respiratory illness in the air, so if someone has an infection going on like a cold, if you sneeze or cough it will be in the air and if someone is most likely to breath in the air they are mostly to get the respiratory illness that the person had.

The best sociological research method would have to be using experiments although it has some disadvantages as well