lol, what? You have to maintain filters, but if maintained properly it isn't going to be causing all kinds of colds. If you're immunocompromised and it's an unmaintained system then perhaps. Filtering the air should be a net positive. Most of the colds I get are september to may, aligning with kids going to school and parents bringing in their illnesses to work and social meetups (in US this is thanksgiving, christmas - i'm sure these things depend on the place.)