system
Given the following post, respond as if you're commenting on Reddit:
human
What determines when a viral infection is no longer contagious?

Covid-19 patients can test positive for up to months after being infected but the CDC guidelines state that the virus is most likely not contagious after 10 days. How is someone who still has detectable amounts of covid-19 in their nose or saliva no longer able to pass it on to someone else?
gpt
It's no longer contagious when you're not producing enough infectious particles in the airways needed to spread virus to another individual. Ebola virus has been found to replicate within the eye of long haul carriers but no evidence indicates these people are capable of spreading virus. If replication is localized to a protected niche then the chance of it aersolizing or spreading through bodily fluids (ebola) is low. Also, PCR methods only detect RNA so it doesn't tell you if infectious particles are being produced. Long haulers likely have infectious particles but not in areas that increase the chance of spread.