Case investigation and contact tracing are core public health strategies for controlling and preventing the spread of infectious diseases. Case investigation involves detecting and notifying individuals with suspected or confirmed infection and eliciting information on the individuals who were in contact with that case and may therefore have been exposed to infection. Contact tracing is initiated after contact elicitation and involves locating, notifying, and interviewing the contacts of suspected or confirmed cases. Case investigation integrates health promotion activities and linkages to health care and other support services to help cases manage their illnesses and prevent further transmission. Similarly, contact tracing includes sharing information to help contacts understand their risk of exposure and providing guidance to protect their health and prevent transmission if they become infected.
While neither case investigation nor contact tracing is a novel public health intervention, the scale and urgency required by the SARS-CoV-2 (COVID-19) global pandemic presented significant challenges for how these traditional public health strategies have been implemented and expanded nationwide. This article discusses the challenges and opportunities of case investigation and contact tracing in controlling COVID-19 transmission and summarizes how these strategies were used by governmental public health agencies in the US COVID-19 pandemic response from late January through August 2020. An examination of this early phase of response indicates that health agencies faced challenges in scaling up contact tracing capacity to the numbers of staff needed, developing guidance and protocols, and revising those as more was learned about the virus, defining differences between work functions, gaining public acceptance of governmental outreach to contacts, and characterizing the utility of contact tracing during outbreak mitigation. Opportunities included promoting the use of technology in public health programs and advancing health equity and community engagement in public health efforts.
Cornerstones of Communicable Disease Control
Case investigation and contact tracing have been cornerstones of infectious disease control and prevention in the United States since the 1930s, when they were used to control syphilis. Since then, case investigation and contact tracing have been used by health departments at all levels of government to prevent the spread of common infectious diseases, such as sexually transmitted infections (STIs) and tuberculosis, and to prevent transmission of novel, emerging, or rare diseases such as Ebola.1,2 In governmental public health agencies nationwide, the work of case investigation and contact tracing is routinely performed by Disease Intervention Specialists (DISs), whose job activities often combine contact tracing and case investigation. In addition to STIs and tuberculosis, DISs are deployed to respond to outbreaks of measles, hepatitis, and other infectious diseases. Prior to the COVID-19 pandemic, the DIS workforce was already under significant strain due to decades of declining public health funding leading to reduced case investigation and contact tracing capacity.3 As a result, health departments have reported that their DISs are overburdened and underresourced.4,5 Early in the pandemic response, it was clear that the existing numbers of the DIS workforce would not be sufficient to perform case investigation and contact tracing at the scale needed for COVID-19. The approaches health agencies implemented to supplement and expand this workforce are described later in this article.
DISs work on the front lines of disease prevention and control, connecting those who test positive for an infection to health care professionals and following up with individuals who were exposed to a positive case to notify them of their exposure. They also inform cases and contacts of the need to take additional public health actions, such as obtaining testing or treatment services, or in the case of COVID-19, isolating or quarantining. A requisite for effective DIS work is fluency with the languages and cultures of the communities they serve. Ideally, DISs are members of the communities with whom they work and can effectively develop trusted relationships with community members.
Case Investigation and Contact Tracing for COVID-19
After the federal government issued restrictions in late January and February 2020 to limit the entrance of overseas travelers to the United States due to global COVID-19 outbreaks, many state and local health departments began scaling up efforts to contain COVID-19 domestically. As the pandemic spread across the United States, it became clear that containing the COVID-19 outbreak in many states would be difficult, if not impossible, without aggressive implementation of mitigation strategies, such as widespread social distancing policies and business closures. In March and April 2020, most states implemented stay-at-home orders, the social and economic impacts of which were experienced across the country. Public health professionals and leaders turned to early lessons learned from other countries that had successfully contained and mitigated COVID-19, such as China, South Korea, and Germany, to identify thresholds for “reopening,” or relaxing, stay-at-home orders and other restrictions. Increasing case investigation and contact tracing capacity emerged from these reviews as a key requirement for reopening.6–8 This recommendation was supported on April 16, 2020, with the release of federal guidelines to states for reopening9 and reiterated a day later when former Centers for Disease Control and Prevention (CDC) director Thomas Frieden issued a 4-part strategy to “box in” (contain) COVID-19.10
COVID-19 modeling studies suggest that the speed, efficacy, and capacity of a jurisdiction to scale up contact tracing impact the success of these programs in controlling outbreaks.11–14 Furthermore, the need to carry out these activities remotely to reduce staff exposure to infection required health departments to innovate and adapt their protocols rapidly. The technology to support disease reporting, case investigation, contact tracing, and case management was also lacking in many jurisdictions, and health departments grappled with uneven adoption of electronic case reporting from laboratories and providers. Cities and states with a high burden of COVID-19 focused case investigation and contact tracing efforts in areas with large outbreaks in congregate living settings and high-density places of employment, such as nursing homes, poultry farms, agricultural production facilities, and meat-packing factories. Case investigation and contact tracing in areas where COVID-19 positivity was lower continued to rely upon contact tracing as a containment strategy. As such, approaches to implementing contact tracing varied from one state to another based on the local phase of response.
Case Investigation and Contact Tracing Challenges
In April and May 2020, the initial spread of COVID-19 on the East and West Coasts of the United States surpassed existing DIS capacity and required quick deployment of additional contact tracers and case investigators. In June and July 2020, a surge of new cases across many states in the southeast and southwest of the United States strained the capacity of nascent COVID-19 contact tracing programs in those regions. Health agencies encountered a range of strategic and operational challenges while establishing, implementing, and adapting case investigation and contact tracing programs to meet the changing demands of the pandemic response. These challenges are described as follows:
Establishing program structure and protocols
Developing a set of standards for the implementation of COVID-19 case investigation and contact tracing programs presented challenges for many jurisdictions early in the response. Partnerships with nongovernmental organizations, schools of public health, and professional services companies developed quickly to support rapid scaling and deployment of contact tracing. Peer-to-peer dissemination of emerging protocols and promising practices was key, and state and local health agencies exchanged workflows, job descriptions, and other materials through professional societies and associations, such as the Association of State and Territorial Health Officials (ASTHO), existing peer networks, online resource libraries, health department Web sites, and other formal and informal means of communication. In May 2020, the CDC released Interim Guidance for Health Departments on Developing a COVID-19 Case Investigation and Contact Tracing Plan, which included technical guidance on COVID-19 contact tracing and case investigation, in addition to considerations for scaling up staffing, building community support, confidentiality and consent, digital contact tracing tools, metrics and monitoring, and more.15 A contact tracing playbook released that same month by Resolve to Save Lives also included operational guidance and a library of resources and sample tools.16 Both resources were augmented as the pandemic response progressed and more was learned about the virus and how it spreads.
The structure of governmental public health authority in each jurisdiction influenced how contact tracing and case investigation programs developed. In states with strong “home rule” governance, contact tracing and case investigation were performed by local (municipal or county) health agencies using a combination of federal, state, and local resources. In these cases, the state role was to support local response and add capacity to help with surge staffing in “hot spots” and to compile data from local agencies statewide for disease surveillance and epidemiology purposes. In jurisdictions with centralized governance, where the state or territorial health agency provides public health services at the local level, state public health staff performed case investigation and contact tracing or contracted the work to other entities. In states with shared or mixed systems, state health agencies conducted these activities in areas without local health departments, while areas with local health agencies provided the services directly with support from states, as needed. State and local health agencies leveraged a mix of funding streams to support expanding case investigation and contact tracing programs, including resources from federal emergency/stimulus packages, other local or state emergency response dollars, and philanthropic organizations.17,18
Characterizing job functions
Early in the pandemic response, the formidable capacity requirements needed to support COVID-19 case investigation and contact tracing led to a separation of the responsibilities traditionally performed in many health agencies by a single DIS job function. In April 2020, the Massachusetts Community Tracing Collaborative (CTC) defined 4 core job functions in its COVID-19 contact tracing and case investigation units, including (1) unit supervisors, (2) case investigators, (3) contact tracers, and (4) care resource coordinators.19 Care resource coordination—similar to case investigation and contact tracing—was not new to public health but was articulated in this structure as a separate job function. Care resource coordinators were tasked with linking individuals to local resources and social support services, such as food and medicine delivery, cleaning supplies, economic supports, and cell phone access during isolation or quarantine.19,20 At the national level, ASTHO and governmental public health partners outlined a recommended national workforce structure with 3 distinct professional tiers to help clarify and describe the functions and scale required for the expanded workforce (see Figure 1), which incorporated contact tracers (the largest segment of the needed workforce), case investigators, and epidemiology/surveillance specialists and medical or clinical consultants.21,22
Expanding the case investigation and contact tracing workforce
Inadequate funding and insufficient personnel to meet COVID-19 case investigation and contact tracing needs posed challenges for health agencies. At the outset of the pandemic, state and local public health agencies employed approximately 2200 DISs in STI, HIV, and tuberculosis programs in the United States.21 Public health experts emphasized the need for a dramatically increased workforce for COVID-19, with national estimates that ranged from 100 000 to 300 000 additional workers.2,23,24 Other population-based benchmarks projected that 30 professionals per 100 000 population would be needed to support COVID-19 case investigation and contact tracing.25 National public health organizations estimated that, when using the case investigation, contact tracer, and epidemiologist/surveillance professional categories (see Figure 1) plus related training and equipment needs, $7.6 billion would be required to support this workforce expansion.22
National public health organizations and subject matter experts used workforce staffing models from China, South Korea, Iceland, New Zealand, and the early work of the Massachusetts CTC, to extrapolate the number of contact tracers needed in the United States, while recognizing that variations in testing capacity, case numbers, adherence to community mitigation measures, and technology implementation would influence these estimates.2,21 To support state efforts to estimate the number of contact tracers needed in a jurisdiction, George Washington University, in partnership with ASTHO and the National Association of County and City Health Officials, as well as Resolve to Save Lives and the CDC, developed online estimators and benchmarks to enumerate and project how many case investigators and contact tracers would be needed by a city or state health agency.26–28 These estimators allow users to modify input variables, such as number of cases, number of contacts per case, follow-up frequency, and shift length, to estimate current or future staffing needs.
Jurisdictions pursued a variety of approaches to build and expand their DIS, case investigator, and contact tracer workforce, including leveraging existing capacity (eg, furloughed government workers, National Guard and AmeriCorps members), partnering with schools of public health and health care organizations, and contracting with third parties to support recruitment, training, and workforce management. For example, agencies supplemented their workforce with school nurses who were on administrative leave due to school closures (Anne Arundel County, Maryland),29 librarians (San Francisco, California),30 and volunteers such as medical or public health students whose classes moved to online instruction or were on summer vacation (Philadelphia, Pennsylvania).31 The CDC complemented these state and local workforce expansion efforts by reassigning and deploying field staff and partnering with the CDC Foundation to place COVID-19 Response Corps positions within health departments.32 As of August 31, 2020, efforts to advocate for federal dollars to support additional case investigators and contact tracers continue to be debated in the US Senate as part of negotiations for a fifth federal stimulus package.
Training new contact tracers, case investigators, and DIS staff
Although no national credentialing process for contact tracers, case investigators, or DISs exists, the Public Health Accreditation Board (PHAB), in partnership with other public health organizations, had explored models for DIS certification starting in 2014.33 In April 2020, ASTHO partnered with the National Coalition of STD Directors (NCSD) to offer a free online training for entry-level contact tracers. The training utilized the job task analysis conducted for the PHAB DIS certification project as the backbone for the curriculum and drew from existing CDC STI and tuberculosis contact tracing training programs, in addition to emerging COVID-19 training examples from state and local health departments. In May 2020, the Johns Hopkins Bloomberg School of Public Health launched an online training for COVID-19 contact tracers as part of a broader New York State and Bloomberg Philanthropies effort to scale up the contact tracing workforce. Both the ASTHO/NCSD and Johns Hopkins courses included introductory content on COVID-19 symptoms, diagnosis, and infectious period; the steps involved in case investigation, contact tracing, isolation, and quarantine; and techniques for effective communication and interviews.34,35
State and local jurisdictions pursued a variety of training approaches, including developing new training programs, as well as adapting or augmenting existing training programs offered by ASTHO/NCSD and Johns Hopkins. Many states also partnered with academic institutions, area health education centers, and regional public health training centers to develop and deliver training programs. The Public Health Foundation, through the TRAIN Learning Network, supported the development of customized training packages by allowing health agencies to combine existing courses with jurisdiction-specific protocols and scripts on one platform. ASTHO and NCSD also supported member jurisdictions by sharing their course files directly with health agencies to allow their customization based on state needs. The CDC funded and realigned new and existing cooperative agreements with national organizations and academic partners to standardize training for the contact tracing workforce. Through these cooperative agreements, ASTHO and the National Network of Disease Intervention Training Centers were tasked with developing and expanding knowledge and skills-based training programs for case investigators, contact tracers, and supervisors.36 Together, these efforts will enhance the knowledge and skills of this evolving and expanded workforce.
Public acceptance and participation
The success of COVID-19 case investigation and contact tracing programs depends on the ability to successfully reach individuals, elicit accurate information on contacts, and encourage full adherence to isolation and quarantine recommendations. With the need to rapidly staff up contact tracers and case investigators in the early COVID-19 response, ensuring local language and cultural fluency of case investigators and contact tracers may have been neglected, likely affecting public acceptance and contributing to delays in successful outreach to cases and contacts. A broad range of behavioral, structural, and sociopolitical factors can impact individual willingness or ability to participate in case investigation and contact tracing.37 Reports of low contact tracing call pickup rates highlighted some of the challenges associated with remote contact tracing. Scams imitating contact tracing calls may have further discouraged individuals from answering unknown calls.38 Concerns about privacy or government overreach can also influence hesitancy to disclose contacts or follow isolation and quarantine procedures. In some cases, distrust and disinformation resulted in hostility and threats against contact tracers.39 Structural challenges, such as the inability to work from home or take paid work leave, lack of access to child- or adult care alternatives, and certain living situations, can also affect individual adherence to isolation and quarantine recommendations, even if public health is successful in making contact with the individual.
State and local health departments have implemented a variety of approaches to address these challenges. Several states took legislative action to explicitly state that participation in case investigation and contact tracing was voluntary; conversely, there were also instances where legal action was taken to enforce participation.40,41 More often, though, health departments addressed participation challenges by developing communication messages to raise awareness and acceptance of case investigation and contact tracing activities. Messages were translated into local languages, encouraging the public to “answer the call,” and informing them of what they could expect from public health outreach (see Figure 2).42,43 Other approaches to address participation challenges included proposing state legislation to ensure the privacy and confidentiality of those participating in case investigation and contact tracing,40 in addition to providing support services such as childcare, food delivery, and temporary housing to address some of the structural barriers to isolation or quarantine.
Experts have recommended approaches for encouraging participation in contact tracing, including partnering with trusted community leaders, offering incentives for participation, optimizing interviewers' skills, and developing communication messages.44 Forthcoming research conducted by Harvard University with support from ASTHO, the CDC, and the National Public Health Information Coalition will characterize public opinions toward contact tracing, variations by race and ethnicity, and potential communication strategies to improve acceptance of and participation in governmental public health efforts. Areas of future research should include an examination of whether DISs were more effective in eliciting information about contacts and building trust than others, and what factors were supportive of effective case investigation and contact tracing.
Balancing case investigation, contact tracing, and outbreak mitigation
Public health experts have described case investigation and contact tracing as sharper, or more precise, tools for COVID-19 containment and suppression than the blunter instruments used in community mitigation such as stay-at-home orders and business closures.45 As the COVID-19 epidemic evolved in the United States, however, the suitability of using these precision tools during mitigation phases was called into question, given the scale of community transmission and the resources that would have been required to trace potential contacts.46 In June and July 2020, soaring COVID-19 case numbers strained state and local case investigation and contact tracing program capacity. Additional barriers early in the response included inadequate testing supplies and delays in test result turnaround times, both of which can impact the effectiveness of case investigation and contact tracing efforts.11 Experts started to question the tipping point at which COVID-19 positivity rates would be too high for case investigation and contact tracing to make an impact due to pervasive community transmission, a question that has yet to be resolved by practitioners.
Research suggests that when implemented together, contact tracing and social distancing work synergistically to move an outbreak back into containment.47 Implementation of case investigation and contact tracing does not need to reach everyone exposed to COVID-19 to make a positive impact on reducing community transmission. In fact, modeling suggests that identification and tracing of even half of symptomatic cases and their contacts could reduce transmission to levels that would allow for loosening of community distancing policies.48 Additional research is needed to inform recommendations for when case investigation and contact tracing are most appropriate during pandemic response in both the containment and mitigation phases. Guidance is also needed to inform the planning and implementation of these programs, given limited testing capacity or delays in obtaining test results. For example, when widespread community transmission or testing delays lower the effectiveness of case investigation and contact tracing programs, health officials might nevertheless consider building their disease investigation workforce reserves in anticipation of moving into suppression phases, while focusing contact tracing efforts in key locations such as long-term care facilities and schools.
Opportunities for Public Health Case Investigation and Contact Tracing Programs
The development and expansion of COVID-19 case investigation and contact tracing programs present opportunities for health departments to optimize disease investigation and prevention efforts through the identification, implementation, and evaluation of promising practices and technology solutions. As difficult and deadly as the COVID-19 pandemic has been, it has allowed for new conversations about building up and investing in the governmental public health infrastructure to further advance health equity, promote healthy and resilient communities, and expand the public health workforce of the future.
Several promising program models have developed during the early stages of the response. The Massachusetts CTC was announced in early April and emerged as a prominent model for program implementation.49 The CTC workflows, staffing organization, care resource coordination, communication, and community engagement approaches were adopted and adapted by many health departments. Their implementation partner, Partners In Health, subsequently formalized technical advisory relationships with Illinois, Ohio, North Carolina, the Navajo Nation, and several local jurisdictions to support contact tracing program efforts.50 A model with a cross-jurisdictional dimension was launched in late April 2020, with the announcement of New York State's contact tracing program, which would be carried out in coordination with neighboring New Jersey and Connecticut. The program has benefitted from funding and recruitment support from Bloomberg Philanthropies, technical assistance from Resolve to Save Lives, and training development from Johns Hopkins University.51 A community-centered model, the Baltimore Health Corps, was announced in June 2020 with the aim of building local resilience by addressing the intersection of the health and economic crises caused and amplified by the pandemic. The program, which is supported by the Rockefeller Foundation and several public and private funders, will provide unemployed Baltimore residents with sustainable career paths and training as community health workers, while expanding contact tracing, education, and outreach capacity.52
Promising practices from early program models include engagement of community stakeholders and inclusion of care coordination and social support services to facilitate adherence to isolation and quarantine. Contact tracing collaboratives in Massachusetts, North Carolina, and Oregon drew from a broad stakeholder base to support program activities, such as local and Tribal health authorities, community-based organizations, academic partners, advocacy groups, and insurance plans.19,53,54 Care resource coordinators, as originally defined by the Massachusetts CTC model, emerged as key personnel tasked with identifying the needs of cases and contacts and connecting individuals to social, financial, and mental health resources. Contact tracing programs in Tribal communities similarly highlighted the importance of providing wraparound services, such as food, water, and medicine delivery, in addition to alternative isolation/quarantine sites when needed.55
Advances in technology
Although technology cannot replace the critical role of the public health workforce, an array of technology tools can be implemented to automate or accelerate aspects of the case investigation and contact tracing workflows. Implementation of these technologies requires assessment of privacy and consent considerations, community and stakeholder engagement, analysis of operational issues, and ongoing evaluation to monitor effectiveness.56 In the early stages of the pandemic response, most state health departments worked to adapt existing or acquire new tools to support case management and workflow coordination. A variety of these tools were custom-made to streamline COVID-19 data collection and case management. For example, Sara Alert was developed by the MITRE Corporation to support health agencies, monitor cases and contacts, track the development of symptoms, flag when an individual fails to submit a daily report, and determine when they may discontinue isolation or quarantine.57
Proximity tracing/exposure notification tools, which rely on Bluetooth or GPS capabilities to identify and automate notification of potential exposures, have emerged as another category of technology with the potential to enhance case investigation and contact tracing. Modeling suggests that exposure notification through a mobile phone application might be more effective in controlling COVID-19 than by manual contact tracing, though the efficacy of the technology also depends on the proportion of the population using the application.58 As of late August 2020, a total of 6 states had launched jurisdiction-level or pilot applications based on the Apple/Google exposure notification programming interface, with Virginia becoming the first state to launch statewide.59,60 No assessment of the efficacy of these applications in supporting governmental public health efforts is available as of yet.
Engaging communities to advance health equity
The COVID-19 pandemic has underscored racial and ethnic inequities, with communities of color experiencing a disproportionate burden of COVID-19 infection, hospitalization, and death.61 As jurisdictions build case investigation and contact tracing programs, there is a great need to base these programs on community engagement models that involve impacted communities at each stage of program development, implementation, evaluation, and improvement. Active engagement of the community and partnership with local resources, such as community-based organizations and university-based community health extension programs, can support improved program outcomes and trust building, while advancing health equity goals and longer-term community resilience efforts.
DIS programs stress the need to recruit staff from the frequently diverse communities the agency serves. Some jurisdictions have adopted this principle for COVID-19, developing requirements that contact tracers represent the cultural and linguistic characteristics of the community and that programs recruit from local workforce development programs.40 The Baltimore Health Corps pilot described earlier serves as a community-based model for the equitable employment of new contact tracers. Chicago's Contact Tracing Corps will similarly support workforce development among racial and ethnic minority populations by distributing grants to community-based organizations to recruit within communities that have historically experienced employment barriers and have been most impacted by the pandemic.62 Expert recommendations on integrating community-based workforce principles in case investigation and contact tracing programs emphasize the importance of recruiting workers that reflect the racial and ethnic diversity of impacted communities, investing in community health workers, and providing training and skills-building opportunities that lead to pathways for career advancement.63
Implications for Policy & Practice
- While variations in state governance structure and communities preclude the development of a one-size-fits-all approach for COVID-19 case investigation and contact tracing programs, lessons learned from DIS programs, guidance and resources from national partners, and peer-to-peer exchange of promising practices can support jurisdictions encountering early implementation challenges.
- Jurisdictions should consider replicating implementation approaches from emerging program models, including engaging a broad array of community stakeholders in program planning and implementation, recruiting and investing in personnel that reflect the cultural diversity of the communities they serve, and incorporating care coordination and support services as part of a comprehensive program.
- The expansion of case investigation and contact tracing presents opportunities to test innovative program models, leverage community engagement approaches to promote health equity and community resilience, and modernize technology systems that can serve as force multipliers for traditional case investigation and contact tracing.
- Further research is needed to assess program models and innovations developed thus far in the response to the COVID-19 pandemic, approaches for improving public acceptance and participation, and implementation strategies during containment and mitigation phases and in the context of limited testing capacity/testing delays.
This article describes the lessons learned and experiences of governmental public health agencies in the early months of the COVID-19 pandemic related to case investigation and contact tracing, two fundamental public health strategies for controlling infectious diseases. Rapid mobilization of these programs presented many strategic and operational challenges, in addition to an array of opportunities for health departments to innovate. A limitation of this article is that data on early implementation challenges and successes were not collected in a systematic manner. While successful program models have been documented in other countries and characterized anecdotally in the United States, a structured, nationwide data collection is needed to better inform decision making and implementation in the United States. As COVID-19 spreads across the country with no currently available vaccine, case investigation and contact tracing will continue to be critical to state and local outbreak response, meriting sustained investment and ongoing research.
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