system
Given the following post, respond as if you're commenting on Reddit:
human
If the coronavirus (sars-cov-2) spreads through aerosols flying out of people's nose/mouth, why do we need a sample from deep inside the nose to detect it instead of just taking a saliva/snot sample from people?
gpt
Testing kits that check for the presence/absence of a virus work best if your sample is likely to have a lot of virus in it.  There’s more virus deep inside your nasal cavity than in your mouth.  There’s still plenty of virus in your mouth to infect someone, but not enough to produce a conclusive positive on a test.