From Johns Hopkins Bloomberg School of Public Health:
Contract tracing is a core public health function that public health agencies have done for years. Diagnostic tests can confirm whether a person is infected with an illness. Contact tracing involves finding out who the infected person had contacts with so that those individuals can be alerted that they are at a risk of developing the illness and at risk of potentially infecting others in the community.During contact tracing, the contacts of the infected person are generally called up, asked if they're feeling sick, and advised to self-quarantine for a period of time. During the quarantine period, the health of the contacts can be monitored and health care or other services could be provided to them if they do develop symptoms. Also, it is important to make sure that people who have been exposed to the illness are not circulating in the community and further spreading the disease.
Anita Cicero, JD, is deputy director of the Center for Health Security at the Johns Hopkins Bloomberg School of Public Health.