photo: An empty park in New Rochelle, a suburb of New York City hit by a spike in coronavirus cases.
An empty park in New Rochelle, a suburb of New York City hit by a spike in coronavirus cases. Yuki Iwamura/Bloomberg

Urban density does play a role in disease transmission. But rural areas and suburban sprawl aren’t necessarily safer spaces to ride out the Covid-19 crisis.

Alexis Kaiser always planned on renting out the house that came with the 250-acre Oklahoma farm that she and her husband bought in 2015. Her sister thought the idea would never work — 65 miles from the nearest airport, the three-bedroom split-level house seemed too remote.

But the listing fared well on Airbnb. Now Kaiser is tapping into a new strain of social anxiety in order to hit it bigger. As cases of a respiratory illness caused by a novel coronavirus spread throughout the U.S., Kaiser is advertising her abode as a “Covid-19 Safe House” on Craigslist in cities with large infection clusters.

“Don’t just hunker down to get through the pandemic, turn this frightening time into a family get-away in the country,” urges the ad she posted to Craigslist in the San Francisco, Seattle, and New York City areas last week. “In the wake of the likely lockdowns and quarantines about to be faced by city-dwellers across America, you need a safe place for your family to live.”

Kaiser isn’t the only one branding rural property as an answer to urban coronavirus fears. A 40-acre compound in Northern California’s Sierra foothills is listed for sale with a hat tip to Covid-19. “Preppers Paradise,” reads another pandemic-branded Craiglist housing post. Airbnb listings around the world describe themselves as “coronavirus-free.”

While it’s too soon to detect any rise in demand for exurban housing related to Covid-19 — the data lags by four to six weeks, according to the California Association of Realtors — Kaiser and others are correct to observe a swell in anxiety about the health risks of urban life. “People who are self quarantining in the suburbs can at least go in their backyards,” tweeted the New York Times’ Taylor Lorenz on Tuesday. “Being stuck inside a NYC apt is only one step above a cruise ship.” Similar sentiments have made their way to the Beltway. “Gotta hope our tremendous sprawl compared to Italy will help us some too,” tweeted Vox writer Matthew Yglesias about the possibility that coronavirus will take a lighter toll in the U.S. than it has in other nations.

As maps like this show, major metropolitan areas are bearing the brunt of the Covid-19 infections spreading across North America. And that makes sense: Though there’s no way to know for sure how the virus arrived, it almost certainly came by way of an international flight to a major airport (or several of them). But while infectious disease spreads faster where people are more densely clustered — hence the strategy of social distancing to contain the coronavirus — that doesn’t necessarily make suburban or rural areas safer, health experts say.

“What we’re seeing is this virus is spreading very fast, and no community is completely removed,” says Cecile Viboud, a senior research scientist specializing in epidemiology and populations at the National Institutes of Health.

That is not to say that cities aren’t Petri dishes — they are. Relative to rural areas, urban centers do provide stronger chains of viral transmission, with higher rates of contact and larger numbers of infection-prone people. And historically, urbanites paid a price for this vulnerability.

“There was a health penalty when you lived in cities,” says Roger Keil, a professor of urban studies at York University in Toronto who wrote recently wrote in The Conversation about the urban frontiers where new infectious diseases flourish. Measles, whooping cough, tuberculosis and other viruses were particularly rampant in early 19th century cities, before better sanitation, vaccination and wider access to healthcare cleaned them up.

And in the pre-globalized era, the countryside did indeed confer some degree of defense. Eva Kassens-Noor, a professor of urban planning at Michigan State University, has studied the 1918 influenza pandemic to better understand the role that population density and other geographic variables play in pandemics. For a 2013 paper in the International Journal of Health Geographics, she and her colleagues found that a population density of 175 people per square mile served as a threshold between higher and lower mortality rates for influenza in India. People living in places with a population density above this threshold were better off getting out of Dodge.

For millennia, urbanites with means did just that. Back in the 14th century, writer Giovanni Boccaccio’s book The Decameron focused on a troupe of wealthy Florentines — the pandemic preppers of their era — escaping the Black Death that festered in the city by holing up in a country home on the city’s hilly outskirts.

But things have changed. Modern transportation networks have made the population shield that rural areas once provided much more porous. Now that humans and freight can travel from, say, Hong Kong to Los Angeles in less than 13 hours — and arrive by vehicle to somewhere sparsely populated hours after that — outbreaks can happen just about anywhere. New pathogens tend to arrive sooner in global hubs, but that doesn’t mean they can’t quickly reach rural locales and proliferate from there, says Benjamin Dalziel, a professor of integrative biology at Oregon State University who studies population dynamics.

“Cities with big airports are definitely importing more cases than cities without,” he says. “But it’s not like all the epidemiological sparks would stay there.”

Or, in Keil’s words: “The idea that we can go to countryside to protect ourselves is a bit of a myth, because it doesn’t exist like it used to.”

Meanwhile, rural and exurban areas have their own unique health challenges. For one, new zoonotic pathogens frequently emerge in pastoral places where humans come into contact with animals. And in the U.S. (and many other countries), rural populations are relatively older, making them more at risk for falling seriously ill from Covid-19. More than one in five older Americans lives in rural places. Those living outside cities also have more limited access to health care generally: Rural residents live much further from hospitals than their urban or suburban counterparts, and more of them list access to good doctors as a major community problem. While a disciplined city can overcome its population density disadvantage by canceling mass gatherings, small towns cannot so easily tweak their spatial health disparities. San Francisco can live without Warriors games; a rural hospital can’t be built overnight.

“Rural populations have less means to contract it [coronavirus], but rural populations have less means to treat it,” Kassens-Noor says.

When it comes to other, more familiar infectious diseases, cities benefit from higher vaccination rates and the accompanying phenomenon known as “herd immunity.” If a large enough percentage of a population has received vaccination to an infectious disease, the community can effectively stop its transmission to vulnerable people or those who didn’t get the shot. In a 2015 paper for Infection Ecology and Epidemiology, epidemiologist Carl-Johan Neiderud showed how coverage rates differ across city and county lines. In Indonesia, for example, more people have the measles vaccination in urban areas (80%) than in rural areas (67%).

This isn't a universal trend, and socioeconomic factors play an important role in both attitudes about and access to vaccines. (Famously, many high-income parts of California contain large numbers of unvaccinated households.) In Chandigarh, India, herd immunity tracks closely with residency and status: 74% of children in urban areas had full immunization by age 2, compared to 63% in rural areas and just 30% in slums. Herd immunity depends on everyone playing along, which is why anti-vaccination adherents are such a threat to vulnerable people in big populations. (There is no vaccine against Covid-19 yet, but herd immunity will likely matter a lot if and when this coronavirus resurfaces.)

Smaller cities can also suffer more acutely from infectious disease than big ones, at least when it comes to the flu. A 2018 paper published in Science, co-authored by Dalziel and Viboud, found that mid-sized metropolitan areas such as Nashville tend to experience shorter and more intense outbreaks of influenza relative to big cities such as New York or Miami. Larger urban populations, the researchers found, provide a greater degree of herd immunity, slowing the spread of the disease through the community and counteracting the role that humidity plays in the spread of flu. Larger urban hospitals also tend to be more capable of handling an influx of sick people.

Of course, Covid-19 is a different bug than the one that killed between 17 and 50 million people worldwide from 1918 to 1920, or the modern variants that resurface during flu seasons. The 1918 influenza outbreak was particularly brutal because it happened in 1918: Social support structures were limited, treatments were relatively primitive, global war fostered illness, and the germ theory of disease was still not well understood. The population-density threshold for influenza mortality in early 20th century India that Kassens-Noor identified doesn’t tell us much about what to do with Covid-19. After all, the population density of, say, Oklahoma City is much, much higher than 175 people per square mile. (The census gives the population density for broader Oklahoma County as 1,013 people per square mile — so OKC is far too urban to dodge an epidemic.)

Dalziel and Viboud both stressed that health researchers are just beginning to understand the transmission dynamics of Covid-19. But it looks like the first cases detected in Italy, Germany, and the U.S. were all on the urban periphery. Some U.S. hot spots — Kirkland, Washington, and New Rochelle, New York — are suburbs of major cities. While it’s too early to detect any consistent pattern in the spread of the novel coronavirus, “what those data underscore is the the fact that you’re not necessarily safe in the suburbs,” Dalziel says. “Those are counter-examples to the idea that it’s just happening in cities.”

Kaiser, the Oklahoma Airbnb host, acknowledges that no one place can guarantee invulnerability to this new pandemic. Still, her listing sounds like an idyllic locale for a destination quarantine — there’s a 14-acre fishing pond and a horse arena. “It seemed like a good way to market the house,” she says. “For someone who has the financial capacity to get away and work from home, here’s your chance to spend a month out on a farm, and avoid some of the trauma we’re seeing in other countries.”

But while the CDC recommends decreasing social contact to limit the spread of the virus, that’s just as doable in a downtown apartment as a countryside manor. Says Viboud: “If you’re staying at home and limiting outside contact, you’d achieve the same purpose.”

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