On March 15, the governor of Washington
called the Seattle area the “hotbed of this outbreak.”
“Code Red,”
blared the tabloid cover of the New York Post eight days later.
And this weekend, the
Tampa Bay Times forecast
that Florida, where the governor has not imposed statewide stay-at-home
measures, would “see tens of thousands of infections in the coming
weeks” from the coronavirus pandemic.
Two months after the
first case of Covid-19 was confirmed in the United States,
the virus
has sprung from its initial toeholds and started to shift the country’s
infection map — from one of pockmarked hotspots to one that blankets
the entire nation. Detroit. New Orleans. Dallas. These are among the
cities that could be the next hubs of the U.S. emergency, and where the
virus has likely been spreading for weeks.
As the outbreak rolls across the country, residents are asking: Who will be hit next? And how fast and how hard?
“It’s very feasible we’re going to see multiple city- or state-level
outbreaks across the country in the next few weeks and months,” said
Maia Majumder, a computational epidemiologist at Boston Children’s
Hospital. “They will start at different times and they will peak at
different times.”
Experts told STAT that a host of factors are at play: demographics
like the age and health of the population; proximity and connections to
other regions; and how densely people live, whether in crowded apartment
buildings or more secluded family homes. There are also factors that
can be addressed through action, like local response efforts and
physical distancing requirements.
Other elements are impossible to predict. With outbreaks, chance
occurrences can push one city’s crisis to the forefront, like Seattle’s
was early on.
“Part of the reason we found it in Seattle is also an element of bad
luck, in the sense that it seemingly quickly jumped into a nursing home,
and there were fatalities, so we caught it,” said Samuel Scarpino, an
assistant professor at Northeastern University’s Network Science
Institute. “It was probably spreading in other parts of the U.S. We just
didn’t see it because those places didn’t have those early fatalities.”
As epidemiologists track the infiltration of the coronavirus in the
United States, their efforts have been hampered by flawed information.
The bungled rollout of testing has created a gulf in our knowledge about
where and how widely the virus has spread — and where a simmer is
starting to boil over.
Models showing how other cities could soon face the health care demands that New York hospitals are experiencing now
helped convince President Trump on Sunday to extend physical distancing recommendations through April.
“When you look at all of the states together, all of them are moving
at exactly the same curves,” Deborah Birx, the physician coordinating
the White House coronavirus response, said Monday. “And so, that’s why
we really believe this needs to be federal guidance, so that every state
understands that it may look like two cases today — that become 20,
that become 200, that become 2,000.”
A major factor in determining which places are hit soonest is where the virus is likely to land first.
Local outbreaks get “seeded” when cases are imported there, but
there’s an inherent randomness at the earliest stage of an outbreak. If
three infected travelers from Wuhan — the Chinese city where the
outbreak is thought to have originated — had landed on the same January
day in three different U.S. cities, one might not have spread the virus
to anyone; one might have spread it to a few people but the transmission
petered out there; and one might have passed it to a few people, who
passed it to a few more people, which created a cluster of cases, and on
from there.
As we try to anticipate the path of the outbreak, experts told STAT
that the more imported cases a location has, the more likely some are to
ignite ballooning chains of transmission. It helps explain why the
Seattle area and San Francisco Bay Area — which have strong ties to Asia
— were home to some of the
first confirmed cases of community spread of the virus. As Europe lit up with infections and Americans abroad fled home, more cities on the East Coast started to be affected.
Experts are quick to caution, however, that the cities that seem to
have had an explosion of cases aren’t necessarily the only places with
transmission.
The coronavirus (SARS-CoV-2 is its scientific name) starts with a slow burn.
People infected
might not show symptoms for five or more days, but during that time,
the virus can be passed to others. By the time enough people get sick
enough to get on health systems’ radars, cases could be spreading
unchecked. It takes much longer to go from one case to 1,000 than to go
from 1,001 cases to 2,000.
“Large numbers of cases may suddenly appear, but a large epidemic has
not occurred suddenly,” Ben Cowling, a University of Hong Kong
epidemiologist, told STAT in an email. “It has probably built up over
many weeks.”
The picture of an outbreak in any given place on a given day is more
like a Polaroid coming into focus from a few weeks ago than a snapshot
of the spread of the virus that day — particularly because of the U.S.
testing problems.
Take, for example, the Seattle area. Experts say Seattle
leapt onto the radar
not because it was necessarily ahead of other cities, but because there
was more information there, and a more dramatic impact. Crafty
researchers, frustrated by the lack of coronavirus testing,
uncovered cases by adapting a separate influenza surveillance project,
showing the virus was moving through their community. The outbreak also
struck a nursing home, sending many people to the hospital with what in
some cases became fatal respiratory infections — generally, older
people are
more likely to suffer severe Covid-19 infections — and signaled the virus’ presence.
A s
the viral spread picks up speed, another factor that will influence
which places are hit the hardest is when and how aggressively local
officials implement physical distancing policies, experts said.
China was able to prevent the kind of crisis that happened in Wuhan —
where the health care system was overwhelmed — from taking place
throughout the country in part because of its aggressive lockdowns.
Keeping people away from each other means the virus can’t spread among
them. It’s why experts are urging leaders in regions that do not think
they have broad spread of the virus yet to implement physical distancing
measures now — to save lives that could otherwise be lost a month from
now.
“The effects will be seen weeks down the road,” said Caroline Buckee,
an epidemiologist at Harvard’s T.H. Chan School of Public Health. For
people who think that distancing measures are not needed in their
communities yet, she said, “that is extremely naïve. Everywhere should
be taking social distancing very seriously, because nowhere is immune to
this virus.”
More than 30 states have told residents to stay at home as much as
possible, though governors in Pennsylvania, Texas, and Florida are among
those who have limited their orders to certain counties or left it up
to local authorities to issue such orders. Because of resistance from
some governors, some experts have called on the Trump administration to
strengthen its recommendations to more enforceable actions.
There are tentative signs that existing distancing measures —
particularly when implemented early — might be having an impact. In the
Boston area,
a “superspreader” event
at a conference in late February made it clear a problem was looming.
Epidemiologists started tracking cases, and local and state leaders
moved fairly quickly to convince people to stay home. Cases have
continued to increase, but the moves may have pushed the peak of the
Massachusetts epidemic
out a few weeks, giving hospitals more time to prepare.
“The hope is that it minimizes it,” Scarpino said. “We still have another week [until we] know how the measures are working.”
In the Bay Area, where local leaders imposed the country’s first “shelter in place” orders in
mid-March, experts are also
watching closely to see if the region’s
infection curve will flatten.
If the region’s hospitals avoid the fate that New York’s are now
facing, one potential explanation is that New York’s infections were
seeded a little earlier and its distancing measures started a little
later. When outbreaks grow exponentially, those differences matter
greatly.
“Did the Bay Area, for instance, import cases in smaller numbers and
later than New York?” said Joseph Lewnard, an epidemiologist at
University of California, Berkeley.
Another concern for regions that haven’t yet seen major outbreaks:
The virus is likely to travel next to cities with close connections to
the initial hotspots. Officials in Houston, for example, have
watched worryingly
as cases in nearby New Orleans have grown, given the number of people
who travel back and forth between the two cities. The spread of the
virus in Atlanta has raised concerns that it could become more
widespread throughout the South.
This is why some
governors
are asking people arriving in their states to quarantine themselves for
two weeks. The federal government on Saturday recommended that most
residents of New York, New Jersey, and Connecticut
refrain from traveling.
“The probability of nobody transmitting the virus becomes very, very,
very low if you have a lot of people infected,” Lewnard said.
Experts describe outbreaks migrating in “traveling waves,” typically
following patterns of transit and connection among communities. As those
waves widen and pulse out from more cities, they can quickly start
converging over the whole country.
“Right now it’s no longer a traveling wave,” Buckee said. “Right now
it’s everywhere in the United States. Maybe not everywhere, but it will
be soon.”
Once the virus does take hold in a community, a host of factors can color what the outbreak looks like.
The age of the population is a clear factor. One hypothesis for
Italy’s high death rate, for example, is that it is the second oldest
country in the world. South Korea’s data of those infected skew young,
but that might be because its outbreak was seeded in a religious
community that was generally young and was then quickly
brought under control.
Demographics are not fate, however. Japan’s population is the only one
older than Italy’s, but its death rate has remained low.
The underlying health of a community will also shape how much harm
Covid-19 inflicts. Heart and lung diseases, diabetes, and other chronic
conditions are, like age,
risk factors for more severe disease. Puerto Rico, Maine, and Florida have the
highest percentage of residents 65 and older, while Oklahoma, Alabama, and Mississippi have the
highest death rates from heart disease.
Access to care and hospital resources also vary widely across the United States. A Washington Post analysis
showed a tenfold difference in ICU capacity among different regions.
Whether a region’s climate matters remains an open question. Other
viruses that cause respiratory infections do not transmit as efficiently
in hot, humid settings. But some experts are skeptical that the weather
in the South, for example, will protect the region, given that this is a
new virus that no one has immunity to. It also spread easily in the
warm climate of Singapore.
Then there’s density. It’s thought that the crowdedness of New York —
where people squeeze into subways and even the parks are packed —
contributed to the spread of the virus there. Experts also pointed to
another type of density: how many people share a single residence,
whether that’s families or roommates. Data from China showed the virus
slipped easily among these closest of contacts, and as distancing
measures go into effect, the contagion could move indoors as well.
“In some sense transmission has been taken off the streets and pushed
back into family units,” Mike Ryan, the head of the World Health
Organization’s emergencies program, said Monday. He added that ideally,
people who were sick would be isolated outside their homes to avoid
spreading it to their families.
As the impact of the virus starts to be felt more dramatically in
more U.S. cities, attention will turn away from the earlier epicenters.
But that doesn’t mean that places we once thought of as the eye of the
storm are in the clear.
Jay Inslee, the governor of Washington,
told CNN on Sunday his state was seeing some modest success in bending its curve. But, he added, “we have a long, long way to go.”
The coronavirus is washing over the U.S. These factors will determine how bad it gets in each community
