The aim of contact tracing is to trace back sources of infection by asking questions. It is an important part of slowing the progress of the epidemic. The staff in the contact tracing team phone people who have tested positive. They give them instructions about the measures they need to take (isolation), ask about possible sources of infection, support requirements (e.g. shopping) and about close contacts during the contagious phase, and resolve any questions. They then get in touch with all close contacts to verify the contact and, if necessary, to tell these people to quarantine. Contact tracing mainly sees to the needs of people in isolation and quarantine by telephone. The COVID Care App is another resource for looking after people in isolation or quarantine in the Canton of Basel-Stadt.