Case Investigation and Contact Tracing

Case investigation and contact tracing have been used for decades to slow or stop the spread of infectious diseases and are essential in controlling the transmission of infectious diseases, including COVID-19. In nearly all countries, the number of COVID-19 cases and contacts has outpaced the capacity of the public health system to quickly notify and isolate all cases and quarantine all contacts.

What’s the difference between case investigation and contact tracing?

Case investigation is part of the process of supporting patients with suspected or confirmed infection and includes a discussion to help patients recall everyone with whom they had close contact during the timeframe in which they may have been infectious.

Contact tracing lets people know they may have been exposed to an infectious agent and what to do next for their own health and the health of others.

Case investigation and contact tracing involves getting the names of all relevant contacts and following up with them. Case investigation and contact tracing programs for COVID-19 should be tailored to local resources and needs.

How does contact tracing help stop the spread of COVID-19?

Contact tracing slows the spread of COVID-19 by letting people know they may have been exposed to the coronavirus because they were in close contact with someone who tested positive for SARS-CoV-2, the virus that causes COVID-19. Therefore, they should stay home for 14 days. Public health authorities may consider options to reduce quarantine.

Are there different ways to conduct contact tracing?

Traditional contact tracing (also called forward contact tracing): Programs may choose to focus their efforts on traditional contact tracing where the emphasis is on people who were exposed to/had contact with a person who tested positive.

• Ask the infected person who they were in contact with beginning from 2 days before their symptoms started or before the date of their positive test if they did not have symptoms.
• Prioritize case investigation of those people who were recently infected with COVID-19 to rapidly identify infection in those they may have exposed while infectious. Isolating these newly infected people prevents them from spreading the virus to others.

Source investigation (also called backward contact tracing): Programs may choose to focus on, or include source investigation during case investigation. Source investigation places the emphasis on identifying the source of exposure of the person who tested positive.

• Ask the infected person who they’ve been with and where they’ve been during the period 2-14 days before their symptoms started or before the date of their positive test if they did not have symptoms.
• Probability of being infected as part of a cluster is greater than the probability of infecting someone, so it may be more efficient to identify the setting(s) where the infected person could have gotten COVID-19.

Source investigation may be more efficient than traditional contact tracing when the number of cases and contacts outpaces the capacity of the public health system to quickly notify and isolate all cases and quarantine all contacts.