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Test, Trace, Isolate

Contact tracing is a critical piece of the Test, Trace and Isolate strategy to manage the novel coronavirus pandemic.  Contact tracing attempts to slow the community spread of a pathogen by breaking the chain or pathway of infection. For example, epidemiologists estimate that each COVID-19 infected person can, on average, infect two to three people. If each infected person infects just two other people, this first positive case, unchecked, can lead to more than 1,000 COVID-19 total cases in ten rounds of infections. 

Contact tracing is routinely used by public health officials to slow the spread of other infectious diseases such as tuberculosis, measles, Ebola and sexually transmitted diseases. However, the problem confronting public health officials today is the sheer scale of coronavirus in the U.S. – more than one million confirmed and almost 30,000 daily new cases reported on average over the past seven days. 

In addition, coronavirus has several characteristics which make it more difficult than other diseases to trace, and it requires more rapid case and contact identification. Finally, privacy laws in the U.S.  such as H.I.P.A.A., the Health Insurance Portability and Accountability Act  make it harder to quickly adopt some of the technological tools used successfully by other countries. As a result, the U.S. must rely on more “traditional” tracing methods that are labor and time-intensive.

The widespread prevalence of the virus calls for a massive contact tracing effort. This is the conclusion of a new study by the Center for Health Security at Johns Hopkins University and the Association of State and Territorial Health Officials (ASTHO). The study, “A National Plan to Enable Comprehensive COVID-19 Case Finding and Contact Tracing in the US,” estimates a need for an additional 100,000 contact investigators to identify, interview, educate and monitor all contacts of infected cases. 

The National Association of County and City Health Officials (NACCHO) estimate a similar level of contact workers will be required. In a position statement released April 16, NACCO states that the number of workers required for each state and community will depend on the number of future positive cases, the number of contacts per case, ease of contact, and total population size.  NACCHO recommends doubling the number of health professionals, including “disease investigation specialists”, from 15 per 100,000 people “in non-emergency situations” to 30 now, given the scale of COVID-19.  This will allow a quicker and more complete tracing response “within hours versus days for other communicable diseases.”

Applying the NACCHO staff-to-population guidelines suggests the need for about 23 investigation specialists for Evanston and about 4,000 for Illinois. Some states are starting to significantly expand contact tracing resources. Massachusetts recently announced plans to hire 1,000 contact tracing workers. This equals about 15 tracers per 100,000 people for the state.

The State of Illinois reports more than 50,000 confirmed cases and averaged about 2,200 daily new cases the past seven days. Evanston has 328 confirmed cases and averaged 10 daily new cases in this same period.  

How Does Contact Tracing Work?

Over the past 30 days, the Centers for Disease Control (CDC) has published a number of guidelines, protocols and recommendations to help public health officials curb community spread of coronavirus and implement contact tracing programs.

The process works by alerting those who have been in close contact with a recently diagnosed person that they are at risk of incubating the disease and becoming sick and infectious. The CDC defines close contacts as household members, intimate partners, caregivers and anyone who has had close contact for a prolonged period of time (generally longer than 30 minutes).

The contacts are encouraged to stay at home, maintain social distance from others and self-monitor for symptoms for 14 days after the last date of contact. Contacts are tested if they develop symptoms. To protect patient privacy, contacts are not told the identity of the person who may have infected them.

Trained contact investigators, under the supervision of public health department officials, conduct interviews with recently diagnosed cases to identify the contacts, educate and monitor them and to intervene and test if necessary. 

Privacy and Technology

South Korea, Taiwan and Singapore have aggressively used technology and electronic data, such as cell phone GPS records, credit card transactions, medical records, etc. to augment traditional approaches to contact tracing. These countries’ quick adoption of these tools is due to their experience with earlier disease outbreaks, such as MERS (Middle East Respiratory Syndrome) in South Korea in 2005 and SARS (Severe Acute Respiratory Syndrome) in Taiwan in 2003.

Some of these approaches will not work in the U.S. due to privacy protections. However, voluntary, opt-in user agreements for data collection and sharing may make some of these applications possible. For example, the Johns Hopkins and ASTHO report describes a mobile contact tracing app, the C-19, recently introduced in Iceland.  This app is voluntary, with user agreements for data usage and deletions.  New Zealand, for instance, developed a national electronic platform for sharing and updating contact information that is synched with electronic health records. Earlier this month, Apple and Google announced a joint effort to develop contact tracing applications “with user privacy and security central to the design.”

Technology also can be used as a “force multiplier” to leverage the time and the work of contact investigators. The Johns Hopkins and ASTHO report lists work-force multiplying technologies including applications to enable people to easily enter and share their health status and contacts and symptom trackers, such as smart thermometers, to monitor case and contact health status.

Insights from Contact Tracing

Contact tracing can also provide valuable data to determine sources of infection and project future infection rates.

For example, if most new cases are household members of already established cases, this could suggest that future cases may decline.  Conversely, if new cases are from formerly unaffected neighborhoods, worksites or social or religious organizations with many members, this may point to a continued rise in new cases. The presence of many new cases with no link to previously identified infection clusters may be an early indication that the spread is not under control and it is too early to relax social distancing and other mitigation measures.

Contact tracing will be critical to controlling outbreaks that may result after social distancing measures are relaxed.  Early identification and isolation of infected cases and close contacts will allow the rest of society to resume work and daily activities safely.


“A National Plan to Enable Comprehensive COVID-19 Case Finding and Contact Tracing in the US,” Center for Health Security at Johns Hopkins University and the Association of State and Territorial Health Officials, April 10, 2020.

“Building COVID-19 Contact Tracing Capacity in Health Departments to Support Reopening American Society Safely,”  The National Association of County and Health Officials, April 16, 2020.

“Public Health Recommendations for Community Related Exposures,” CDC, March 30, 2020.

“Contact Tracing: Part of a Multipronged Approach to Fight the COVID-19 Pandemic,” CDC, reviewed April 22, 2020.

“COVID-19 Contact Training Guidance and Resources,” CDC, updated April 23, 2020.