Contact tracing


In public health, contact tracing is the process of identifying people who may have been exposed to an infected person and subsequent collection of further data to assess transmission. By tracing the contacts of infected individuals, testing them for infection, and isolating or treating the infected, this public health tool aims to reduce infections in the population. In addition to infection control, contact tracing serves as a means to identify high-risk and medically vulnerable populations who might be exposed to infection and facilitate appropriate medical care. 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. 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.
The goals of contact tracing include:
  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
  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.

    History

Contact tracing programs were first implemented to track syphilis cases in the 1930s. Initial efforts proved to be difficult given the stigmatization associated with sexually transmitted infections. Individuals were reluctant to report infections because they were concerned for their privacy. Revealing partner history and details about sexual activity was challenging as it affected relationships among individuals and community members. In addition, public health officials targeted certain populations such as sex workers, minorities, and at-risk populations further eliciting feeling of fear, shame, and guilt in society. With these negative implications of contact tracing, particularly in the space of sexually transmitted infections, public health officials found it difficult to elicit information from exposed individuals. During the HIV epidemic, many affected person were hesitant to report information, which hindered the efforts to understand HIV and curb the spread. To combat some of the negative stigma associated with contact tracing and STIs, health departments sometimes referred to contact tracing as partner notification in the 1980s. 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. This definition evolved from identifying infected individuals to including a comprehensive program that encompasses counseling and medical care to treat the infection.
The official title, contract tracers, was first implemented in the United Kingdom during the smallpox outbreaks. Dedicated individuals served on a surveillance-based team to curb the spread of disease. This process served as a blueprint for other public health agencies to have a formalized program. The United States soon followed and enacted a contact tracing program for the prevention of infectious diseases which included TB, HIV, SARS, and now SARS-CoV-2.

Steps

Contact tracing generally involves the following steps as provided by CDC:
  1. Notification of exposure: An individual is identified as having a communicable disease. This case may be reported to public health or managed by the primary health care provider. Ideally, all notification should be done within 24 hours of exposure. If contacts are not individually identifiable, broader communications may be issued, like media advisories. Communication with the contacts will be initially done through digital methods including texts and email. Efforts to inform the contacts remotely should be exhausted before considering an in-person communication. During this process, it is imperative that the identity of the source of exposure must not be revealed to the contact.
  2. Contact interview: 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. Interviews typically follow a template which include demographics, symptomology, pre-existing conditions, and timing of exposures to ensure consistency across all contact tracing efforts. Interpreters and source materials in different languages are utilized to accommodate persons with different cultural backgrounds.
  3. Recommendations for close contacts: Once contacts are identified, public health workers contact them to offer counseling, screening, prophylaxis, and/or treatment. Contacts are provided education on concepts of quarantine, isolation, signs and symptoms of disease, and timely testing. If applicable, contacts should wear appropriate personal protective equipment to reduce to transmission of disease.
  4. Assessing feasibility of self-quarantine and support: Contacts may be isolated or excluded if deemed necessary for disease control. Challenges for this process include access to resources during quarantine such as food, water, and safe living environment. People with special roles lack the convenience practicing quarantine given their daily responsibilities. Examples include, single parents, caregivers, and individuals with toddlers. Social services and ancillary support from the government become crucial to maintaining measures of quarantine and isolation. Contacts should be made aware whether or not the quarantine or isolation is voluntary or mandatory. Depending on the nature of the disease of interest, governments can issue legal orders to maintain integrity of contact tracing.
  5. Medical monitoring: 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. Ideally, contacts are checked upon daily for signs and symptoms of disease by contact racers. An alternative would be having the contacts report daily to their assigned official. This is usually done through digital platforms such as email and text. If a contact is symptomatic, a case investigator is assignment to direct the individual to the appropriate testing and treatment. This stage of contact tracing is highly dependent on resource availability.
  6. Contact close out: This stage is dependent on the duration of quarantine for people with and without symptoms. The ideal number of days for quarantine and isolation are determined by the health agencies. Once the contact adequately completes the quarantine/isolation for the defined number of days, they can be closed out. Next steps such as returning to work and participating in social activities are discussed.

    Application

Contact types

The types of contacts that are relevant for public health management vary 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. This information is crucial for investigating congenital syphilis cases for example. For blood-borne infections, blood transfusion recipients, contacts who shared a needle, and anyone else who could have been exposed to the blood of the index case are relevant. This information becomes relevant for health systems to keep track of high risk populations and medical errors, unavoidable and preventable. 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. Understanding the pathology and transmissibility of the disease guides the approach to contact tracing strategy.

Outbreaks

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.
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. Contact tracing can help identify the etiology of a disease outbreak. In 1984, contact tracing provided the first direct evidence that AIDS may be spread by an infectious agent during sexual contacts. The infective agent has since been identified as HIV.
Diseases for which contact tracing is commonly performed include tuberculosis, vaccine-preventable infections like measles, sexually transmitted infections, blood-borne infections, Ebola, bacterial infections, and novel virus infections. Contact tracing has been a pillar of communicable disease control in public health for decades. With each outbreak and disease presenting with its own challenges, contact tracing is an adaptable tool used by authorities to identify, notify, and curb transmission of infections.