I've also been asked about this. Farting is not thought to be a way in which COVID-19 is spread. Certain medical procedures pose a genuine risk of creating infectious aerosols - procedures that may aerosolise lots of virus particles from the key site, the respiratory tract. https://twitter.com/andrewjtagg/status/1247087520849920000

Contact & droplet precautions are appropriate when doing anything around bottoms in the context of COVID-19 (assuming no AGP is going on at the same time); for UK this means gloves, apron, fluid-resistant surgical mask, & eye protection based on risk assessment (splash risk etc.)

Evidence to date suggests the behaviour of SARS-CoV & SARS-CoV-2 (COVID-19) may not be identical, & many are struggling to isolate viable (infectious) virus from faeces. Detection of SARS-CoV-2 RNA/RNA fragments in faeces is not the same as proving a significant transmission risk

Oh and my usual reminder (I don't care it it's repetitive): good hand hygiene remains as important as ever, and not just for preventing COVID-19. We all need to remember to clean our hands more often and do it thoroughly, wherever we are.