system
Given the following post, respond as if you're commenting on Reddit:
human
If you catch a cold, is there an easy way to know or guess which virus is causing it?
gpt
Not only is there no easy way to tell, there’s no hard way to tell either. Even in a research setting, using tailored highly sensitive PCR and other techniques, a significant minority of “colds” never have a causative agent linked to them.

There no simple way to tell at all.  Symptoms may give a very crude estimate, but there’s so much overlap that it’s not much more than old wives’ tales.