If people are offering first aid to someone who may have symptoms of Covid-19 they should follow the current guidance (see link below and avoid giving rescue breaths unless they have adequate protection.

https://www.gov.uk/government/publications/novel-coronavirus-2019-ncov-interim-guidance-for-first-responders/interim-guidance-for-first-responders-and-others-in-close-contact-with-symptomatic-people-with-potential-2019-ncov