The History of Contact Tracing and the Future of Public Health

In the years after the elucidation of the germ theory of disease in the late 19th century, public health officials began to explore new strategies to reduce transmission of infections. Public health programs tracking infectious disease transmission became an important element of infection control and response to epidemics. From an historical perspective, contact tracing focused on the idea that if those infected could be identified, isolated, and persuaded to report their contacts, outbreaks could be slowed and, in some instances, stopped.

As a result, contact tracing has frequently been used to address infectious diseases over the course of the past century. A recent review by El-Sadr et al.¹ traces the use of contact tracing for syphilis and gonorrhea, tuberculosis, HIV, Ebola, and, most recently, COVID-19. A wide range of approaches, however, fall within the general rubric of contact tracing. These strategies have been based on the authority of the state to surveil and track epidemics; require physicians and public health agencies to report certain diseases; and identify individuals for surveillance, investigation, and contact by public health authorities.²

The first major contact tracing programs targeted syphilis (Figure 1). Historically, the tracking of sexually transmitted infections led to stigmatization. Tracing required individuals to name sexual contacts, revealing intimate details about sexual relationships, as well as perceived indiscretions and infidelities, sometimes compromising marriages, families, other personal relationships, and employment. In the 1930s, tracing of syphilis infections required what officials often called “shoe leather epidemiology” to hunt down cases (often targeting prostitutes, minorities, and immigrants), as well as the interrogation of “suspects,” mandating Wassermann tests, and eliciting “confessions.” Contact tracing augmented the existing fear, shame, guilt, and stigma of syphilis.³ Not surprisingly, already vulnerable communities have often viewed these programs as both intrusive and dangerous. The threat of public exposure, isolation, and possible quarantine often encouraged individuals to avoid the “public health police.” This historical legacy of contact tracing programs continues to serve as an important obstacle to their widespread and effective implementation. Recognizing that such approaches could have the effect of limiting the voluntary identification of contacts, public health officials during the HIV epidemic began to adopt “partner notification programs,” which emphasized the contact case’s personal and ethical responsibilities to the health of their sexual partners.

FIGURE 1—

Contact Tracing Chart From the New York City Health Department, 1938

THE PROBLEM OF EFFICACY

Although contact tracing has a clear logic, its potential effectiveness has often depended on the biological characteristics of infectious organisms. The disease-specific variables that influence the efficacy of contact tracing include the mode of transmission, the relative transmissibility of the organism, the length of an asymptomatic phase, and the length of time the agent is transmissible. Effectiveness is also related to the availability and accessibility of sensitive and specific laboratory testing regimes (and the timely access to results), as well as the potential to use treatments to render individuals noninfectious. Contact tracing is also dependent on contextual social, political, and ethical issues. These vary from the approach and skill of public health personnel to elicit names of contacts to complex questions of the social meanings, cultural contexts, and significance of the disease. Together, these biosocial variables make effective tracing challenging and sometimes impossible. For example, in many instances during the COVID-19 pandemic, individuals have been unaware of when they first acquired an infection and may have had hundreds of anonymous “contacts” before they became symptomatic. Highly transmissible, COVID-19 often outran programs for tracing contacts.

The efficacy of contact tracing, however, requires greater clarity about its goals and outcomes. As a public health strategy, contact tracing has historically depended on the participation and cooperation of individuals and communities. Such collaborations are sensitive to ethical considerations of protecting others who may be infected, as well as political assessments of the role of the government in preventing the spread of infectious diseases. Fear of punitive isolation or social stigma has often served as a critical obstacle to participation; in these cases, tracing programs have been seen as acts of surveillance and discipline by the state.^4,5

LOOKING BACKWARD, LOOKING FORWARD

The COVID-19 pandemic offers an important opportunity to assess a variety of approaches to what has been broadly deemed “contact tracing.” The pandemic has illuminated many of the strengths and weaknesses in current practices in the United States and other countries around the world. Before the advent of vaccines, there was particular interest in contract tracing to reduce transmission of the virus through testing and isolation of the infected. As we look to the future, the COVID-19 pandemic now offers a series of “natural experiments” to assess the value of tracing, especially because policies, technologies, and strategies varied greatly across states and nations.^6,7

In particular, the pandemic spurred two critical innovations in approaches to contact tracing. For the first time in history, countries widely used digital technologies to identify possible exposures. Several countries (South Korea, Singapore, Australia, and New Zealand, among others) quickly introduced new digital tracing systems through smartphone applications that could alert individuals to exposures; encourage immediate testing; and, if a person was found to be infected, promote isolation. The comparative efficacy of these programs has yet to be fully determined and requires further research. But in many nations, especially the United States, uptake tended to be relatively low, severely limiting the value of this approach. Individuals who declined to use these applications typically cited concerns about privacy and surveillance.⁸ For this type of digital tracking to be successful, it is estimated that 60% adoption would be required. This will require clearer assurances of privacy and anonymity, as well as greater understanding of the potential social value of digital public health applications.^4,9

In the United States, where skepticism of state authority has been particularly high, it is important that contact tracing programs be seen as serving the interests of individuals, their families, and communities. Several state programs instituted in 2020 sought to embed these values in their approaches, centering attention on informing individuals of their infections; educating them on best practices to avoid transmission; assuring that they had resources to isolate; and providing social support, including food and other necessities. The shift from a public health approach based upon police powers of the state to one that emphasizes community social engagement and support, especially among those most vulnerable, offers an important lesson.¹⁰ In such programs, which used the potential of what the late Dr. Paul Farmer described as “accompaniment,” contact tracing assumed the goals of dedicated community health work, assuring that the needs of patients with COVID-19 and their contacts were identified and that material resources, social support, and advocacy were available.^11,12

This approach has important implications beyond the future of contact tracing. It offers an orientation to public health that relies on collaboration, participation, and the provision of information and services, which erodes traditional notions of state discipline, isolation, and criminalization, often centered on vulnerable minority populations. Furthermore, it suggests that contact tracing can be integral to building trust and confidence in public health efforts that serve individuals, families, communities, and wider populations. The capacity to identify individuals experiencing infectious diseases and help them access medical care and protect their contacts through prevention or treatment is at the core of public health. But how this is done has enormous implications for health outcomes, reducing disparities, promoting equity, and how we imagine the future of public health.