Contact Tracing – The Infectious Disease Resource Center

In public health, contact tracing is the process of identification of persons who may have come into contact with an infected person (“contacts”) and subsequent collection of further information about these contacts. By tracing the contacts of infected individuals, testing them for infection, treating the infected and tracing their contacts in turn, public health aims to reduce infections in the population. Diseases for which contact tracing is commonly performed for include tuberculosis, vaccine-preventable infections like measles, sexually transmitted infections (including HIV), blood-borne infections, some serious bacterial infections, and novel infections (e.g. SARS-CoV and SARS-CoV-2). The goals of contact tracing are:

To interrupt ongoing transmission and reduce spread of an infection
To alert contacts to the possibility of infection and offer preventive counseling or prophylactic care
To offer diagnosis, counseling and treatment to already infected individuals
If the infection is treatable, to help prevent reinfection of the originally infected patient
To learn about the epidemiology of a disease in a particular population

Contact tracing has been a pillar of communicable disease control in public health for decades. The eradication of smallpox, for example, was achieved not by universal immunization, but by exhaustive contact tracing to find all infected persons.^[1] This was followed by isolation of infected individuals and immunization of the surrounding community and contacts at-risk of contracting smallpox.

In cases of diseases of uncertain infectious potential, contact tracing is also sometimes performed to learn about disease characteristics, including infectiousness. Contact tracing is not always the most efficient method of addressing infectious disease. In areas of high disease prevalence, screening or focused testing may be more cost-effective.

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.

People in close contact with someone who is infected with a virus, such as the Ebola virus, are at higher risk of becoming infected themselves, and of potentially further infecting others.

Closely watching these contacts after exposure to an infected person will help the contacts to get care and treatment, and will prevent further transmission of the virus.

This monitoring process is called contact tracing, which can be broken down into 3 basic steps:

Contact identification: Once someone is confirmed as infected with a virus, contacts are identified by asking about the person’s activities and the activities and roles of the people around them since onset of illness. Contacts can be anyone who has been in contact with an infected person: family members, work colleagues, friends, or health care providers.
Contact listing: All persons considered to have contact with the infected person should be listed as contacts. Efforts should be made to identify every listed contact and to inform them of their contact status, what it means, the actions that will follow, and the importance of receiving early care if they develop symptoms. Contacts should also be provided with information about prevention of the disease. In some cases, quarantine or isolation is required for high risk contacts, either at home, or in hospital.
Contact follow-up: Regular follow-up should be conducted with all contacts to monitor for symptoms and test for signs of infection

Steps in Contact Tracing

Contact tracing generally involves the following steps:

An individual is identified as having a communicable disease (often called the index case). This case may be reported to public health or managed by the primary health care provider.
The index case is interviewed to learn about their movements, whom they have been in close contact with or who their sexual partners have been.
Depending on the disease and the context of the infection, family members, health care providers, and anyone else who may have knowledge of the case’s contacts may also be interviewed.
Once contacts are identified, public health workers contact them to offer counseling, screening, prophylaxis, and/or treatment.
Contacts may be isolated (e.g. required to remain at home) or excluded (e.g. prohibited from attending a particular location, like a school) if deemed necessary for disease control.
If contacts are not individually identifiable (e.g. members of the public who attended the same location), broader communications may be issued, like media advisories.

Although contact tracing can be enhanced by letting patients provide information, medication, and referrals to their contacts, evidence demonstrates that direct public health involvement in notification is most effective

Relevance of contacts[edit]

Contact tracing during a Cholera outbreak in Bangladesh (2014): FETP investigators interview the mother of an index case patient.

The types of contacts that are relevant for public health management vary with the communicable disease because of differing modes of transmission. For sexually transmitted infections, sexual contacts of the index case are relevant, as well as any babies born to the index case. For blood-borne infections, blood transfusion recipients, contacts who shared a needle, and anyone else who could have been exposed to blood of the index case are relevant. For pulmonary tuberculosis, people living in the same household or spending a significant amount of time in the same room as the index case are relevant.^[3]

Outbreaks[edit]

Although contact tracing is most commonly used for control of diseases, it is also a critical tool for investigating new diseases or unusual outbreaks. For example, as was the case with SARS, contact tracing can be used to determine if probable cases are linked to known cases of the disease, and to determine if secondary transmission is taking place in a particular community.^[4]

Contact tracing has also been initiated among flight passengers during the containment phase of larger pandemics, such as the 2009 pandemic H1NI influenza. However, there continue to be large challenges in achieving the goals of contact tracing during such chaotic events.^[5] Development of better guidelines and strategies for pandemic contact tracing continues.^[6]

Mobile phones[edit]

Main article: COVID-19 apps

On 10 April 2020, Apple and Google, which, combined, account for most of the world’s smartphones, announced coronavirus tracking technology for iOS and Android.^[7]^[8] Relying on Bluetooth Low Energy (BLE) wireless radio signals for contact tracing,^[9] the new tools would warn people about others they’d been in contact with who are infected by SARS-CoV-2. Various protocols, such as Pan-European Privacy-Preserving Proximity Tracing (PEPP-PT),^[10] Decentralized Privacy-Preserving Proximity Tracing (DP-PPT/DP-3T),^[11]^[12] Contact Event Numbers (CEN), Privacy Sensitive Protocols And Mechanisms for Mobile Contact Tracing (PACT)^[13] and others, are being discussed to preserve user privacy. Corresponding coronavirus apps will be released in May and enhanced later in 2020.^[8]