Density, Cities, and Disease — a Complex Adaptive System
Stephen Luoni, University of Arkansas
June 10, 2020
What is a healthy city after the COVID-19 pandemic? One instinctive line of thinking argues that cities will have to become less dense to mitigate the effects of this and future pandemics. Historically, people fled the city for the safety of a lower-density countryside upon infection of a virgin community by an unfamiliar disease. Before modern public health, plague, cholera, smallpox, viruses, and other transmissible diseases could kill most of a city’s residents, when, urban economist Edward Glaeser observes, “cities were killing fields”. Old World cities evolved into civilized disease pools where diseased-experienced populations found an equilibrium with some microparasitic communities that grew less virulent over time. Endemic diseases to which urban adult populations evolved immunity remained otherwise lethal to non-experienced ruralites and people in different biomes. In chronicling historical instances of the genetic tug of war between parasites and hosts to shape disease behavior, historian William McNeill in Plagues and Peoples notes that: “such factors as climate, human diet, human density, and patterns of movement must have also impinged upon the sensitive and unstable equilibrium between disease organisms and their human hosts.”¹ Hence, interrelationships among populations, place, and infection profiles are a complex adaptive system. Unlike linear systems, each component does not convey an understanding of the whole system’s behavior. Therefore, we need to put aside the reliance on one component — density — as a predictor of infection outcomes.
Despite our emerging and incomplete understanding of the multivariate influences shaping the COVID-19 landscape, we do know that density can be a factor in disease transmission, but density is not a factor in disease virulence. Since coronavirus is a respiratory disease, a growing body of research is examining the relationship between air quality and COVID-19. A new study shows air pollution having a stronger correlation than density with both transmission and mortality rates in early global pandemic hotspots.² The Po Valley in Northern Italy has Europe’s highest concentration of air pollution and its highest rate of COVID-19 fatalities. Based on mounting evidence that a viral spillover from animals to humans occurred in Wuhan years before 2019, the study speculates that air pollution in Wuhan (some of the worst in China) could have played a role in the virus’ mutation to a more lethal strain than the coronavirus found in the common cold.³ Other comorbidity factors resulting from poor diet, tobacco use, lack of physical activity, poverty — and in COVID-19’s case, age — may prove to be greater determinants of disease behavior than density. Accordingly, metropolitan areas with high automobile use and characteristically poor air quality — including low-density regions — may be more susceptible to COVID-19’s respiratory effects.
High density is not intrinsically a barrier to successful disease control. But absent public health and its multidimensional analyses, pandemics can be unnecessarily deadly as illustrated by the New York metropolitan area’s shockingly high coronavirus fatality count, currently at more than 21,000.⁴ Nonetheless, Manhattan, the world’s seventh densest city fabric⁵, has a per capita coronavirus infection rate half that of surrounding boroughs with far less density.⁶ Meanwhile, in the dense capital cities of east and southeast Asia, all with intense travel networks to China where COVID-19 originated, the pandemic’s impacts have been impressively minimized. Singapore, Hong Kong, Taipei, Kuala Lumpur, and Seoul show that density requires a vigilant public health system in managing disease risk. Singapore, a city state of nearly six million people, overcame one of the twentieth-century’s highest tuberculosis rates by foregrounding public health in its nation building process since breaking away from Malaysia in 1965. Notwithstanding a population density equivalent to New York City, where more than 90 percent of Singaporeans live in high-rise apartments and 60 percent travel by train, Singapore recorded 25 deaths from COVID-19.⁷ Nearby Vietnam, a country of 97 million people living in dense cities like Hanoi and Saigon, has had zero COVID-19 deaths, despite being one of the first countries to report cases.⁸ Asian communities’ disease experience with Ebola, Avian Flu, and SARs outbreaks over the last generation equipped them to set the standard for containing COVID-19.
Modern public health likely made possible the rise and economic dominance of the contemporary dense southeast Asian city. Their location within a tropical biome of a characteristically high disease gradient demands astute knowledge networks in disease monitoring and control. Despite perceptions of authoritarianism among the West, affluent Asian communities exemplify information-rich governance structures, the kind of learning organizations the U.S. once had in its Centers for Disease Control. Public health can make the dense city resilient, and COVD-19 reminds us that public health and risk management are fundamental dimensions of effective governance. Density, cities, and disease constitute valuable information feedback loops in shaping civilizing processes.
So, the city is both a problem and a solution. Scientist Geoffrey West reinforces this point through examination of systems scaling from which he discovered universal properties governing the behavior of cities. West found that with every doubling of city size, cities grew 15 percent more wealthy, productive, innovative, and sociable while requiring 15 percent less infrastructure. The good comes with the bad as doubling also brings 15 percent more poverty, violent crime, and infectious disease.⁹ Density, therefore, has compounding effects. It uniquely underwrites health-inducing investments in public transit, walkable infrastructure, micromobility, and public park systems not feasible in low-density environments with single land uses. Frederick Law Olmsted’s legacy of early 20th century landscape urbanism networks connecting urban parks of all scales with riparian corridors and greenways, new street type classifications, urban neighborhoods, conservation preserves, and civil infrastructure in stormwater management and water supply offer us lessons in adapting a vocabulary of city-building components to new needs, including those for social distancing, ecosystem services (e.g., greenhouse gas regulation), and a lower-energy future.
Without density, would cities had developed the great urban sanitation and water supply systems of the 19th century? Without density, would cities have developed urban public-transit systems, a milestone achievement in equity providing mobility and access to all? Without density and its wealth surpluses from industrialization, would cities have developed science-based medical institutions that hastened vaccination discoveries, antimicrobial research, and the epidemiological transition which has not only minimized impacts from infectious disease, but doubled lifespans over just a century in advanced economy nations? Without density, would we have witnessed the invention of modern non-combustible building technologies, including fire-retardant systems that eliminated once common urban conflagrations? The list could go on, but the next stage of inquiry into threats like pandemics is to establish minimums and maximums in balancing advantages of density with its diminishing returns. We have built our world and our prosperity around density, and our most robust solutions continue to evolve within its context.
[1] William H. McNeill. Plagues and Peoples, Anchor Books, 1976, p 123.
[2] Riccardo Pansini and Davide Fornacca. “Higher virulence of COVID-19 in the air-polluted regions of eight severely affected countries”, medRxiv. Accessed June 6, 2020, https://doi.org/10.1101/2020.04.30.20086496.
[3] Ibid.
[4] Accessed June 9, 2020, https://projects.thecity.nyc/2020_03_covid-19-tracker/.
[5] https://en.wikipedia.org/wiki/List_of_cities_proper_by_population_density.
[6] New York City Health Department COVID-19: Data. Accessed May 10, 2020, https://www1.nyc.gov/site/doh/covid/covid-19-data.page.
[7] Accessed June 6, 2020, https://www.gov.sg/article/covid-19-cases-in-singapore.
[8] Chris Humphrey. “Vietnam crushed the coronavirus outbreak, but now faces a severe economic test”, The Guardian, May 5, 2020, https://www.theguardian.com/global-development/2020/may/06/vietnam-crushed-the-coronavirus-outbreak-but-now-faces-severe-economic-test
[9] Geoffrey West. “Scaling: The surprising mathematics of life and civilization”, Santa Fe Institute, October 31, 2014, https://medium.com/sfi-30-foundations-frontiers/scaling-the-surprising-mathematics-of-life-and-civilization-49ee18640a8.
