thumb|upright=1.4|Contact tracing attempts to find all contacts of a confirmed case, in order to test or monitor them for infection. The goal is to stop the spread of a disease by finding and isolating cases.

In public health, contact tracing is the process of identifying people who may have been exposed to an infected person ("contacts") and subsequent collection of further data to assess transmission. In doing so, public health officials utilize contact tracing to conduct disease surveillance and prevent outbreaks. In cases of diseases of uncertain infectious potential, contact tracing is also sometimes performed to learn about disease characteristics, including infectiousness.

  1. Interrupting ongoing transmission and reduce the spread of an infection
  2. Alerting contacts to the possibility of infection and offer preventive services or prophylactic care
  3. Alerting the general public about exposures or outbreaks of COVID-19, Measles, TB, etc.
  4. Offering diagnosis, counseling and treatment to already infected individuals
  5. If the infection is treatable, helping prevent reinfection of the originally infected patient
  6. Learning about the epidemiology of a disease in a particular population
  7. Being a tool in multifaceted prevention strategy to effectively curb the spread of an infectious disease.

thumb|Visual depiction of disease spread with and without contact tracing.

History

Contact tracing programs were first implemented to track syphilis cases in the 1930s. Partner notification, also called partner care, is a subset of contact tracing aimed specifically at informing sexual partners of an infected person and addressing their health needs.

Steps

thumb|upright=1.3|A visualization of contact tracing

thumb|upright=1.3|Transmission chains

Contact tracing generally involves the following steps as provided by CDC:

  1. Notification of exposure: An individual is identified as having a communicable disease (often called the index case). Interpreters and source materials in different languages are utilized to accommodate persons with different cultural backgrounds. Understanding the pathology and transmissibility of the disease guides the approach to contact tracing strategy.

Contact tracing has also been initiated among flight passengers during the containment phase of larger pandemics, such as the 2009 pandemic H1NI influenza. Contact tracing played a major role in investigating Ebola virus in the UK in 2014 and monkeypox in the UK in 2018. The eradication of smallpox, for example, was achieved by exhaustive contact tracing to find all infected persons. This was followed by isolation of infected individuals and immunization of the surrounding community and contacts at-risk of contracting smallpox. In 1984, contact tracing provided the first direct evidence that AIDS may be spread by an infectious agent during sexual contacts.

Diseases for which contact tracing is commonly performed include tuberculosis, vaccine-preventable infections like measles, sexually transmitted infections (including HIV), blood-borne infections, Ebola, bacterial infections, and novel virus infections (e.g., SARS-CoV, H1N1, and SARS-CoV-2). traced the sexual contacts of 40 early AIDS patients by sexual contact. The paper concluded that the spread of AIDS may be facilitated by the transfer of an infective agent during sexual contacts.]]

Backward and forward tracing

Backward (or reverse) tracing seeks to establish the source of an infection, by looking for contacts before infection. During the COVID-19 pandemic, the adoption by Japan in early spring 2020 of an approach focusing on backward contact tracing was hailed as successful, and other countries which managed to keep the epidemic under control, such as South Korea and Uruguay, are said to have also used the approach. In the United States, contact tracing had suboptimal impact on SARS-CoV-2 transmission, largely because 2 of 3 cases were either not reached for interview or named no contacts when interviewed. Engagement in contact tracing was positively correlated with isolation and quarantine. However, most adults with COVID-19 isolated and self-notified contacts regardless of whether the public health workforce was able to reach them. Identifying and reaching contacts was challenging and limited the ability to promote quarantining, and testing.

Forward tracing is the process of looking for contacts after infection, so as to prevent further disease spread. Additionally, officials overlooked the effect of mistrust in the government and conspiracy theories regarding the virus on thwarting contact tracing efforts in the U.S.

COVID-19

Contact tracing requires tremendous resources and work hours to effectively contain an infection. The COVID-19 pandemic is an unprecedented period where contact tracing and public health efforts were put to the test. Various countries had different adaptations and outcomes with contact tracing.

When on-demand testing was promoted, increases in negative tests were followed by increases in hospitalizations. Subsequent studies of cases and deaths found the same results. If increased testing were in response to surges, more testing should follow increases in cases, not precede them. An average of 208 extra miles were accumulated in the week following each negative test in U.S. counties. These results suggest that people who tested negative underestimated the risk of exposure when they traveled or visited.

As self-administered, home-based tests became increasingly used as the primary method to detect SARS-CoV-2, fewer cases were reached for case investigation and contact tracing by public health departments. As a result, fewer cases followed contemporary isolation recommendations.

Technology

thumb|Three ways to sign in for contact tracing during the COVID-19 pandemic in Germany

The age of digital contact tracing started gaining traction during the COVID-19 pandemic. In addition, digital applications automate the process and replace the manual steps contact tracers take to track and notify exposed individuals. Manual contact tracing is not suited to detect exposures unknown to the contact, as the process is limited to the interview and known knowledge. This is typically a cloud database that may have specialized features such as the ability to use SMS or email directly within the software to notify people believed to have been in close contact with someone carrying an infectious disease. Utilizing a database, provides benefit to track persons of interest and offers a platforms to look at data points such as race, zip code, and symptoms.thumb|App-based contact tracing during COVID-19.

Software

South Korea became a pioneer in utilizing digital contact tracing tools. Learning lessons from the MERS outbreak in 2015, the government executed a robust contact tracing program. On 10 April 2020, Apple and Google, which account for most of the world's mobile operating systems, announced COVID-19 apps for iOS and Android. Relying on Bluetooth Low Energy (BLE) wireless radio signals for proximity information, the new tools would warn people that they had been in contact with who are infected by SARS-CoV-2.

Limitations

With the use of technology, certain limitations and challenges come with the territory. In Pennsylvania, a digital exposure notification app for COVID-19 was downloaded by 5.7% of population (635,612 people). Unfortunately, only 0.1% of all reported cases in Pennsylvania used the app to notify their potential contacts of exposure during the study period (390 persons), resulting in 233 notifications as compared an estimated 573,298 eligible contacts.

thumb|Sonia Y. Angell, former California Director of Public Health, explains contact tracing during the COVID-19 pandemic.

Challenges with contact tracing can arise related to issues of medical privacy and confidentiality. In the United States, HIPAA is a legal measure for protecting health information. This ensures sharing of only relevant information in the contact tracing process. Contact tracing efforts miss vulnerable and under resourced populations.

Safeguards become topics of contention when designing digital contact tracing tools. Moreover, whether participating in contact tracing efforts should be voluntary or mandatory is another ethical dilemma that adds to the complexity of implementation.