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Introduction

As the world becomes increasingly urbanized and interconnected, infectious diseases—both existing and emerging—pose a serious and rapidly escalating threat to urban populations if left unaddressed. According to United Nations estimates, the global urban population will top 6 billion by the year 2050, with most of that growth occurring in developing countries (Alirol et al., 2011). Along with this exponential urban growth there has been a concomitant surge in the number of people living in urban and periurban slums, as population pressures cause urban centers to grow upwards and outwards. Today, an estimated one in eight people around the world live in slums, and although the proportion of people living in slums has decreased worldwide over the past 15 years, the absolute number is currently approaching 1 billion people, with no sign of that growth abating (UN-Habitat, 2016a).

The urban built environment includes all physical parts of where humans live and work in a city, such as homes, buildings, streets, open spaces, and infrastructure. The urban built environment is a prime setting for microbial transmission, because just as cities serve as hubs for migration and international travel, components of the urban built environment serve as hubs that drive the transmission of infectious disease pathogens (Alirol et al., 2011). The risk of infectious diseases for many people living in slums is further compounded by their poverty and their surrounding physical and social environment, which is often overcrowded, is prone to physical hazards, and lacks adequate or secure housing and basic infrastructure, including water, sanitation, or hygiene services (Ezeh et al., 2017). These conditions harbor an ideal setting for mosquito vector development and

resting sites and the transmission of waterborne diseases. If people in slums do become ill, many of them lack access to health services for treatment. Though slum conditions vary economically and socially across regions and within countries, the populations most at risk will face worsening health consequences if the growth in urban and slum populations is not matched with an increased emphasis on research that brings together disciplines, such as urban planning, public health, environmental health, and social and behavioral sciences. Such action would help further elucidate disease transmission in urban areas and the specific challenges associated with studying and implementing interventions in slums.

WORKSHOP OBJECTIVES

To examine the role of the urban built environment in the emergence and reemergence of infectious diseases that affect human health, the Forum on Microbial Threats at the National Academies of Sciences, Engineering, and Medicine, in collaboration with the Board on Life Sciences, planned the 1.5-day public workshop Urbanization and Slums: New Transmission Pathways of Infectious Diseases in the Built Environment.¹ The following topics were explored during the workshop²:

• The formation, function, and interaction of microbial communities in the urban built environment that affect human health;
• Specific urban built environment characteristics, spatial heterogeneity, and land-use patterns, as well as social and behavioral factors (host and vector movement) that may alter vector distribution and increase or facilitate transmission of infectious diseases;
• Critical opportunities, challenges, and knowledge gaps relevant to translating research findings into practical application of shaping urban environments that prevent and mitigate infectious disease outbreaks;
• Innovative strategies, interventions, and policies for creating sustainable and health-promoting urban built environments that consider structural and socioeconomic determinants of diseases;
• Obtaining valid and reliable data to monitor and evaluate implementation and progress of programs and policies; and

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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 B.

• Collaboration and coordination mechanisms among various stakeholders and across sectors in urban planning, public policy, public health, animal health, environmental health, microbiology, and social and behavioral sciences.

The 1.5-day workshop was held in Washington, DC, on December 12 and 13, 2017. The workshop was co-chaired by James Hughes, professor of medicine and public health at Emory University Rollins School of Public Health, and Mary Wilson, clinical professor of epidemiology and biostatistics at the University of California, San Francisco. Workshop speakers and discussants contributed perspectives from government, academia, and the private and nonprofit sectors. The workshop featured 2 keynote addresses and 11 speaker presentations over two sessions. During the third session, workshop speakers, forum members, and attendees broke into three groups to discuss set themes related to promotion of health and control of infectious diseases in urban built environments.

ORGANIZATION OF THE PROCEEDINGS OF A 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 recommended by individual workshop participants. Chapter 2 features two keynote presentations that explored potential challenges and opportunities for the prevention and control of infectious diseases in an increasingly urban and interconnected world, from both global and local perspectives. Chapters 3 and 4 include presentations and discussions from session 1 of the workshop, which examined social, physical, environmental, and political drivers of infectious disease transmission in the urban built environment. Specifically, Chapter 3 features presentations that explore the link between slums and adverse health outcomes, routes of pathogen transmission in urban buildings, and pathways of pathogens within, into, and out of urban centers. Chapter 4 features presentations that focus on translating conceptual models into practice, with illustrative examples describing efforts against the Ebola virus disease outbreak in West Africa, waterborne diseases in Bangladesh, Zika and leptospirosis in Brazilian slums, and tuberculosis in Cape Town, South Africa. Chapter 5 covers presentations and discussion from session 2 of the workshop, which examined effective interventions and policies for achieving sustainable and health-promoting urban built environments; presenters described experiences with water, sanitation, and hygiene interventions, with slum upgrading and health promotion in India,

and with community engagement against dengue in Mexico and Nicaragua. Chapter 6 explores research gaps to bridge drivers and interventions toward scaling up successful practices, featuring reports from the breakout group moderators and highlights from the large group discussion.