The History of Contact Tracing and the Future of Public Health

Contact tracing strategies for infectious diseases: A systematic literature review

Contact tracing has been a crucial public health strategy for breaking infectious diseases chains of transmission. Although many resources exist for disease outbreak management none address the rationale of contact tracing. This comprehensive review aims to evaluate contact tracing strategies, their effectiveness, and health systems governance across various diseases to inform a disease-agnostic contact tracing guideline. This systematic review was registered with PROSPERO (ID: CRD42023474507) and follows Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Descriptive and interventional studies in the six official United Nations languages were included, excluding modelling studies and animal-to-human transmission. An electronic search was conducted in Embase, Medline, Medline-in-process, and Cochrane libraries from inception to September 2023. The revised Cochrane Risk of Bias Tool and the Risk of Bias in Non-Randomized Studies of Interventions were used for bias assessment. The search yielded 378 studies, primarily from Europe (29.6%) and North America (21.6%) and focusing on diseases such as the coronavirus disease (COVID-19) (47.4%) or tuberculosis (26.7%). 244 (64.5%) studies addressed contact tracing definitions, commonly based on physical proximity, including duration of contact and sexual partnerships (47.6%) and household exposure (27%). Effectiveness was examined in 330 (87.3%) studies, showing variation across diseases and contexts, with only five studies evaluating epidemiological impacts. Socio-cultural aspects were covered in 166 (43.9%) studies, revealing that stigma and public trust may affect the adherence to contact tracing. Health systems governance was discussed in 278 (73.5%) studies, emphasising the need for coordination among international organisations, national governments, and local health authorities, alongside a sustained and adequately supported workforce. This review provides critical insights into optimising contact tracing strategies. Effective contact tracing requires robust health systems governance, adequate resources, and community involvement. Future research should focus on establishing standardised metrics for comparative analysis and investigating the impact of contact tracing on disease incidence and mortality.

Test allocation based on risk of infection from first and second order contact tracing

Strategies such as testing, contact tracing, and quarantine have been proven to be essential mechanisms to mitigate the propagation of infectious diseases. However, when an epidemic spreads rapidly and/or the resources to contain it are limited (e.g., not enough tests available on a daily basis), to test and quarantine all the contacts of detected individuals is impracticable. In this direction, we propose a method to compute the individual risk of infection over time, based on the partial observation of the epidemic spreading through the population contact network. We define the risk of individuals as their probability of getting infected from any of the possible chains of transmission up to length-two, originating from recently detected individuals. Ranking individuals according to their risk of infection can serve as a decision-making tool to prioritise testing, quarantine, or other preventive measures. We evaluate interventions based on our risk ranking through simulations using a fairly realistic agent-based model calibrated for COVID-19 epidemic outbreak. We consider different scenarios to study the role of key quantities such as the number of daily available tests, the contact tracing time-window, the transmission probability per contact (constant versus depending on multiple factors), and the age since infection (for varying infectiousness). We find that, when there is a limited number of daily tests available, our method is capable of mitigating the propagation more efficiently than some other approaches in the recent literature on the subject. A crucial aspect of our method is that we provide an explicit formula for the risk, avoiding the large number of iterations required to achieve convergence for the algorithms proposed in the literature. Furthermore, neither the entire contact network nor a centralised setup is required. These characteristics are essential for the practical implementation using contact tracing applications.

Making the public protect public health: the ethics of promoting collective action in emergencies

Effective public health responses to many infectious diseases require sustained collective action. Communicable disease control in populations can only be achieved by high levels of public compliance with health directives. However, governing authorities have limited options if public compliance is insufficient and collective action is failing. Mechanisms to promote public compliance occur on a spectrum from providing public health advice, offering incentives so people cooperate more, to enacting coercive public health orders and mandates. Because the burdens and benefits of these interventions have patterned distributions across society and raise questions of fairness and legitimacy, they have ethical dimensions. Against the background of government responses to COVID-19, we draw on Amatai Etzioni's compliance mechanisms to analyse the ethics and politics of using state power to drive collective action during public health emergencies. We show how different compliance mechanisms have been applied simultaneously and strategically and that the political and ethical impacts of their interaction warrant particular attention. When considering the adoption of compliance strategies, at the level of individuals and groups, it is important to recognise that intervention uptake will vary based on the threat faced, the characteristics of the population and communities, and local capacity to implement strategies. The use of compliance mechanisms during COVID-19 is also instructive. Significant preparatory work to enculture more restrictive social norms and high levels of public compliance must be undertaken immediately if efforts to sustain collective action against pressing global health problems such as global heating and antimicrobial resistance are to be successful.

Integrating HIV Cluster Analysis in Everyday Public Health Practice: Lessons Learned From a Public Health--Academic Partnership

BACKGROUND

The use of molecular HIV cluster analysis to supplement public health contact tracing has shown promise in addressing HIV outbreaks. However, the potential of HIV cluster analysis as an adjunct to daily, person-by-person HIV prevention efforts remains unknown. We documented lessons learned within a unique public health-academic partnership while guiding workaday HIV prevention efforts with near-real-time molecular cluster analysis.

SETTING

A public health-academic partnership in the State of Rhode Island, the United States.

METHODS

We recorded perceptions of our team of academicians and public health practitioners that were encountered in an 18-month study evaluating the integration of molecular cluster analysis with HIV contact tracing for public health benefit. The focus was on monthly conferences where molecular clustering of each new statewide diagnosis was discussed to facilitate targeted interventions and on attempted reinterviews of all newly HIV-diagnosed persons statewide whose HIV sequences clustered to increase partner naming.

RESULTS

Three main themes emerged: First, multidisciplinary conferences are substantially beneficial for gleaning actionable inferences from integrating molecular cluster analysis and public health data. Second, universal reinterviews were perceived to potentially have negative consequences but may be selectively beneficial. Third, the translation of cluster analysis into public health action is hampered by jurisdictional surveillance boundaries and within-jurisdictional data silos, across which data sharing is problematic.

CONCLUSIONS

Insights from a statewide public health-academic partnership support integration of molecular HIV cluster analyses with public health efforts, which can guide public health activities to prevent transmission while identifying substantial barriers to integration, informing continued research.

Looking under the lamp-post: quantifying the performance of contact tracing in the United States during the SARS-CoV-2 pandemic

Contact tracing forms a crucial part of the public-health toolbox in mitigating and understanding emergent pathogens and nascent disease outbreaks. Contact tracing in the United States was conducted during the pre-Omicron phase of the ongoing COVID-19 pandemic. This tracing relied on voluntary reporting and responses, often using rapid antigen tests due to lack of accessibility to PCR tests. These limitations, combined with SARS-CoV-2's propensity for asymptomatic transmission, raise the question "how reliable was contact tracing for COVID-19 in the United States"? We answered this question using a Markov model to examine the efficiency with which transmission could be detected based on the design and response rates of contact tracing studies in the United States. Our results suggest that contact tracing protocols in the U.S. are unlikely to have identified more than 1.65% (95% uncertainty interval: 1.62-1.68%) of transmission events with PCR testing and 1.00% (95% uncertainty interval 0.98-1.02%) with rapid antigen testing. When considering a more robust contact tracing scenario, based on compliance rates in East Asia with PCR testing, this increases to 62.7% (95% uncertainty interval: 62.6-62.8%). We did not assume presence of asymptomatic transmission or superspreading, making our estimates upper bounds on the actual percentages traced. These findings highlight the limitations in interpretability for studies of SARS-CoV-2 disease spread based on U.S. contact tracing and underscore the vulnerability of the population to future disease outbreaks, for SARS-CoV-2 and other pathogens.

Effectiveness of contact tracing on networks with cliques

Contact tracing, the practice of isolating individuals who have been in contact with infected individuals, is an effective and practical way of containing disease spread. Here we show that this strategy is particularly effective in the presence of social groups: Once the disease enters a group, contact tracing not only cuts direct infection paths but can also pre-emptively quarantine group members such that it will cut indirect spreading routes. We show these results by using a deliberately stylized model that allows us to isolate the effect of contact tracing within the clique structure of the network where the contagion is spreading. This will enable us to derive mean-field approximations and epidemic thresholds to demonstrate the efficiency of contact tracing in social networks with small groups. This analysis shows that contact tracing in networks with groups is more efficient the larger the groups are. We show how these results can be understood by approximating the combination of disease spreading and contact tracing with a complex contagion process where every failed infection attempt will lead to a lower infection probability in the following attempts. Our results illustrate how contact tracing in real-world settings can be more efficient than predicted by models that treat the system as fully mixed or the network structure as locally treelike.

Transformative practice and its interactional challenges in COVID-19 telephone contact tracing in Flanders

This article focuses on transformative interactional practice in COVID-19 contact tracing telephone calls in Flanders (Belgium). It is based on a large corpus of recorded telephone conversations conducted by COVID-19 contact tracers with index patients in the period mid-2020 to mid-2022. The calls were conducted through government-contracted commercial call centers. For nearly 2 years and applied country-wide, this was the most prominent strategy in Belgium for breaking transmission chains. COVID-19 telephone contact tracing with infected patients counts as transformative professional work in two ways. First, in addition to the registration of recent contacts in a relevant time window, the work is oriented to awareness-raising about how patients and their co-dwellers can and should adjust their behavior by attending actively to critical aspects of the pandemic during an individual period of (potential) infection. This is the terrain of advice, interdictions and recommendations about quarantine, isolation, personal hygiene, etc. In addition, the focus on interactional attention indexes patients' affect and emotions (e.g., anxiety, worry, or anger) in a period of health uncertainty and social isolation. The transformative work thus depends on successfully established rapport and empathetic, responsive behavior. Our analysis of the recorded conversational sequences focuses on the complexities of client-sensitive and responsive transformative sequences and highlights the constraints and affordances which surround the interactional task of 'instructional awareness raising' which is central to telephone contact tracing. Specifically, we detail the following dimensions of transformative sequences: (i) how do contact tracers deal with the knowledge status of clients, (ii) their use of upgrading/downgrading formulations, (iii) the use of humor and other mitigating strategies, and (iv) how contact tracers attend to interactional displays of affect and emotion. In a final section, we tie together our observations about the communication of particularized advice in a context of general measures through the twin notions of categorization/particularization-work. The findings in this paper are limited to the first step in the chain of contact tracing, i.e., telephone calls with tested and infected citizens.

Rapid and sustained contact tracing training for COVID-19 in San Francisco: a training model for developing an emergency public health workforce

The City and County of San Francisco was the first municipality in the United States to institute a COVID-19 contact tracing program. The San Francisco Department of Public Health (SFDPH) and the University of California, San Francisco (UCSF) created an outcome-based fully remote contact tracing curriculum using participatory learning methods to train non-public health emergency workers as contact tracers. Between April and December 2020, we trained over 300 individuals in contact tracing skills and procedures over three training phases. Using iterative curriculum design and Kirkpatrick's evaluation methodology, we aimed to ensure high quality and successful person-centered contact tracing. The resulting curriculum consisted of 24 learning outcomes taught with six participatory skills development activities, asynchronous materials, and one-on-one contact tracer support. We collected more than 700 responses from trainees using various evaluation tools across the training phases, and contact tracers interviewed more than 24,000 contacts after training in our program. Our evaluations showed that knowledge and skills improved for most trainees and demonstrated the utility of the training program in preparing trainees to perform person-centered contact tracing in San Francisco. Local health jurisdictions and state health agencies can use this model of curriculum development and evaluation to rapidly train a non-public health workforce to respond to future public health emergencies.

Looking under the lamp-post: quantifying the performance of contact tracing in the United States during the SARS-CoV-2 pandemic

Contact tracing forms a crucial part of the public-health toolbox in mitigating and understanding emergent pathogens and nascent disease outbreaks. Contact tracing in the United States was conducted during the pre-Omicron phase of the ongoing COVID-19 pandemic. This tracing relied on voluntary reporting and responses, often using rapid antigen tests (with a high false negative rate) due to lack of accessibility to PCR tests. These limitations, combined with SARS-CoV-2's propensity for asymptomatic transmission, raise the question "how reliable was contact tracing for COVID-19 in the United States"? We answered this question using a Markov model to examine the efficiency with which transmission could be detected based on the design and response rates of contact tracing studies in the United States. Our results suggest that contact tracing protocols in the U.S. are unlikely to have identified more than 1.65% (95% uncertainty interval: 1.62%-1.68%) of transmission events with PCR testing and 0.88% (95% uncertainty interval 0.86%-0.89%) with rapid antigen testing. When considering an optimal scenario, based on compliance rates in East Asia with PCR testing, this increases to 62.7% (95% uncertainty interval: 62.6%-62.8%). These findings highlight the limitations in interpretability for studies of SARS-CoV-2 disease spread based on U.S. contact tracing and underscore the vulnerability of the population to future disease outbreaks, for SARS-CoV-2 and other pathogens.