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Introduction

The understanding of how infectious diseases are related to noncommunicable diseases (NCDs) has evolved over time. With many challenges to showing the connection between microbial threats and NCDs over the past century, the idea was maintained that most infectious diseases are also acute illnesses and that chronic diseases have noninfectious sources (O’Connor et al., 2006). In the 1970s and 1980s, this thinking began to evolve when Helicobacter pylori was found to induce gastric inflammation (Marshall et al., 1985), and many other linkages began to be exposed, including human papillomavirus and cervical cancer (Hadley, 2006; Burnett-Hartman et al., 2008), hepatitis B and C viruses and chronic liver disease (Hadley, 2006), and Borrelia burgdorferi and chronic Lyme arthritis (Steere et al., 2004). These scientific discoveries spurred the development of more effective prevention and treatment programs that directly targeted the diseases and saved countless lives. With such growing evidence, scientists today believe that a significant portion of chronic diseases may be associated with microbes and infections.

While there has been growing recognition of the breadth of linkages between infectious diseases and NCDs, the two fields continue to be isolated from each other, with the two realms often supported by separate funding streams, studied using divergent research methodologies, and shaped by vertical health policies and programs. This is concerning as epidemics of infectious diseases and NCDs today are increasingly colliding on a global scale, with escalating consequences of mortality and morbidity that are poised to affect huge numbers of people in the coming decades (Marais et al., 2013). The balance of the global burden of disease is shifting toward

NCDs, with increasing numbers of low- and middle-income countries experiencing a double burden of infectious diseases and NCDs (Jamison et al., 2018). In fact, NCDs affect people in low- and middle-income countries disproportionately, where approximately 32 million people are dying from NCDs, with nearly half of those deaths occurring before the age of 70 (WHO, 2018b).

The convergence of infectious diseases and NCDs is becoming more apparent by a constellation of factors. Globalization enables both people and infectious diseases to travel swiftly around the world, while rapid urbanization and increasing interrelationships among humans, animals, plants, and the environment are driving the transmission of infectious diseases and contributing to NCD-related risks (Leon, 2008; Bygbjerg, 2012). Environmental and lifestyle factors such as dietary patterns are decreasing microbial diversity in the human microbiome and increasing NCDs and NCD risk factors (Xu and Knight, 2015; Sheflin et al., 2017; Billingsley et al., 2018). The convergence is also becoming more apparent owing to advances in molecular techniques and immunology, as well as culture methods, laboratory technology, and epidemiological techniques that are uncovering the linkages between microbes and NCDs. However, methodologies and analyses across these techniques must be scrutinized and standardized to ensure valid and reliable results (O’Connor et al., 2006).

The epidemiological transition and scientific advances are blurring the traditional lines between infectious diseases and NCDs. The convergent dynamics among microbes, infections, NCDs, normal health functioning, and shared risk factors are complex and intertwined. The evidence spans a wide spectrum. Some research shows infectious diseases as being a risk factor for developing NCDs (see Chapter 3), while the reverse connection is also seen with NCDs being associated with the development and severity of infectious diseases (see Chapter 4). Multimorbidities involving various permutations of infectious diseases and NCDs also add another layer of complexity. Moreover, the perturbation of the microbiome—such as from diet, other lifestyle factors, and use of antibiotics—has also been shown to affect human functioning and could be a risk factor for the development of NCDs (see Chapter 5). In fact, dozens of chronic diseases have already been associated with the human microbiome, some of which have been cured through microbiome manipulation in animal models (Zheng et al., 2018; Proctor et al., 2019). The field of syndemic research shows how the interplay between diseases is shaped by biological, behavioral, psychological, and social interactions that exacerbate the effect of disease–disease dynamics on human health (Singer et al., 2017) (see Chapter 2).

Research has only begun to reveal the enormous complexity of the microbial world and the extent to which microbes interact with humans and influence human health. Getting a better understanding of these linkages and

bridging cross-sectoral collaborations would help identify further research priorities, develop better targeted prevention and treatment interventions and policies, and leverage existing health systems to effectively respond to both infectious diseases and NCDs to ultimately reduce the public health impact and burden of the convergence from the local to national to global levels.

WORKSHOP OBJECTIVES

On June 11 and June 12, 2019, a planning committee under the auspices of the Forum on Microbial Threats at the National Academies of Sciences, Engineering, and Medicine held a 1.5-day public workshop at The Rockefeller Foundation in New York City, titled Breaking Down Silos: The Convergence of Infectious Diseases and Noncommunicable Diseases.¹ Building on the previous work of the forum (IOM, 2004, 2014), this workshop was convened to explore the growing understanding of how the interplay between humans and microbes affects host physiology and causes NCDs. Peter Daszak, president of EcoHealth Alliance who chaired this workshop, stated that the workshop intends to allow participants to gain a deeper understanding of the continuum between infectious diseases and NCDs, including how this continuum provides new opportunities for prevention and treatment. Naveen Rao, managing director for health and senior advisor to the president at The Rockefeller Foundation, reflected that he comes from a time in which the demarcation between communicable diseases and NCDs was clear, in contrast to the focus of this workshop. From his perspective, he noted that he is interested in how to bring the best data and advances in data science to community health in a way that bridges the emerging divide between people who have access to data as well as better health and people without access to data, who tend to have relatively poorer health. Rao described this workshop as an opportunity to extend the focus beyond health care to a broader concept of health, to a focus on the community, and to a focus on bridging the data divide.

Workshop speakers and discussants contributed perspectives from government, academia, and the private and nonprofit sectors. Specifically, participants discussed the following topics during the workshop²:

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¹ The planning committee’s role was limited to planning the workshop, and the Proceedings of a Workshop was prepared by the workshop rapporteurs as a factual summary of what occurred at the workshop. Statements, recommendations, and opinions expressed are those of individual presenters and participants, and are not necessarily endorsed or verified by the National Academies of Sciences, Engineering, and Medicine, and they should not be construed as reflecting any group consensus.

² The full Statement of Task is available in Appendix A.

• Current knowledge on the known and suspected causal associations between micro-organisms and chronic diseases and conditions, as well as associated issues;
• The evolving understanding of how the microbiome affects the normal physiological functioning of humans and how these interactions vary depending on the population, geographic location, and other biological or environmental factors;
• Research needed to further understand the relationship between micro-organisms and chronic diseases and physiological functions;
• Opportunities for developing new approaches to prevent, detect, and mitigate chronic diseases and to reduce their public health impact and burden;
• Cutting-edge methods and tools as well as study designs being used to explore links between chronic diseases and infectious diseases; and
• Mechanisms to leverage cross-sectoral collaborations and break down silos among various stakeholders from research to practice.

ORGANIZATION OF THE PROCEEDINGS OF THE WORKSHOP

In accordance with the policies of the National Academies, the workshop did not attempt to establish any conclusions or recommendations about needs and future directions, focusing instead on information presented, questions raised, and improvements suggested by individual workshop participants. Chapter 2 includes highlights from the workshop’s two keynote presentations that developed the rationale for convergent action for colliding epidemics and syndemics of infectious diseases and NCDs. Chapters 3 and 4 explore the current state of the science and emerging research on the convergence of infectious diseases and NCDs. Specifically, Chapter 3 features case studies on the possible associations of infectious diseases and microbes leading to the development of NCDs, including the role of oral bacterial infection in Alzheimer’s disease, the contribution of the Epstein-Barr virus to the etiology of autoimmune and inflammatory diseases, and the effect of the microbiome on food allergies. Chapter 4 includes two case studies—one on metabolic syndrome and the risk of enteric infection and the other, converging epidemics of diabetes and tuberculosis—that examine the risks that chronic diseases pose to the development and severity of infectious diseases. Chapter 5 describes the plenary presentation that provides a broader perspective on the microbial dimension to human development and functioning, and the potential it offers for new approaches to human well-being.

The chapters thereafter cover issues on the practical implications of the convergence between infectious diseases and NCDs. Chapter 6 provides

highlights from the panel discussion on how to confront the “blind people and the elephant” metaphor to bridge the silos between infectious diseases and NCDs in the move toward convergent action. Chapter 7 explores strategies for integrating and revamping health care delivery models and interventions to address the convergence. Chapter 8 summarizes the small group discussions on potential strategies and actions to prioritize to advance the research agenda and effectively translate research into policy and practice in the immediate term, and finally Chapter 9 presents visionary statements from three global health experts on their views of top priorities for next steps.

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