It wasn’t until Day 7 of her team’s coronavirus investigation when it dawned on Linda Vail, the health officer for Michigan’s Ingham County, that this was going to be a big one. It had started with just two infections at the college bar on June 18, not long after the state began reopening. But the numbers quickly jumped to 12, then 18, then 34.
As of Friday, she was staring at a spreadsheet with 187 infected at Harper’s Restaurant and Brew Pub.
“The tables were six feet apart, but no one stayed there,” she said. “The DJ was playing music so people were shouting, the dance floor started to get crowded. We had flattened the curve and then boom.”
The East Lansing case is what’s known as a superspreading event — possibly the largest so far in the United States among the general public. Many scientists say such infection bursts — probably sparked by a single, highly infectious individual who may show no signs of illness and unwittingly share an enclosed space with many others — are driving the pandemic. They worry these cases, rather than routine transmission between one infected person and, say, two or three close contacts, are propelling case counts out of control.
More than 1,000 suspected clusters — ranging from the single digits to thousands — have been logged in a database compiled by a coder in the Netherlands. A megachurch in South Korea. A political rally in Madrid. An engagement party in Rio de Janeiro. Nearly all took place indoors, or in indoor-outdoor spaces.
Even as the Trump administration pressures schools to reopen this fall, the latest research suggests that understanding how and why these events occur — and how to prevent them — is key to reopening safely. In recent days, governors from at least 18 states, including Michigan, have backtracked on plans to loosen restrictions due to outbreaks.
But even those efforts may fail if people ignore the most common ways the virus is considered to spread. Transmission, it turns out, is far more idiosyncratic than previously understood. Scientists say they believe it is dependent on such factors as an individual’s infectivity, which can vary person to person by billions of virus particles, whether the particles are contained in large droplets that fall to the ground or in fine vapor that can float much further, and how much the air in a particular space circulates.
Donald Milton, a professor of environmental health at the University of Maryland, and other experts have wondered if superspreading events could be the “Achilles’ heel” of the virus. If we could pinpoint the conditions under which these clusters occur, Milton argued, we could lower the transmission rate enough to extinguish the spread.
“If you could stop these events, you could stop the pandemic,” Milton said. “You would crush the curve.” (...)
As we enter the seventh month of the global pandemic, scientists are still frustratingly in the dark when it comes to key aspects of how the virus is transmitted.
Why, for instance, didn’t the earliest infections in the United States, or the infamous Lake of the Ozarks party, spur lots of cases, while a much smaller gathering at a Michigan bar produced nearly 200? Why out of countless large gatherings held — church services, soccer games, choir rehearsals, and Zumba classes — did only a fraction ignite significant infections?
Part of the uneven spread of the coronavirus — and the phenomenon of superspreading — can be explained by extreme individual variation in infectivity, researchers say.
Some people will not transmit the virus to anyone, contact tracing has shown, while others appear to spread the virus with great efficiency. Overall, researchers have estimated in recent studies that some 10 to 20 percent of the infected may be responsible for 80 percent of all cases. (...)
A growing body of evidence suggests that SARS-CoV2, like other coronaviruses, expands in a community in fits and starts, rather than more evenly over space and time. Adam Kucharski of the London School of Hygiene and Tropical Medicine has estimated that the value of what’s known as the k-parameter — a measure of how much a virus tends to cluster — indicates that just 10 percent of people may be responsible for 80 percent of novel coronavirus cases.
Real world data corroborates the skewed transmission pattern.
In a detailed analysis of outbreaks in Hong Kong, for example, researchers found three distinct groups of incidents. The superspreading individuals, representing 20 percent of the total, were responsible for 80 percent of transmissions. A second group, involving about 10 percent of cases, transmitted the virus to one or two others. The final group, 70 percent, did not infect anyone else at all.
In Israel, investigators looking at 212 cases concluded that they could be linked back to 1 to 10 percent of people. And in an outbreak in a South Korea office tower, investigators found that about 45 percent of 216 workers got the virus from a single person. In the United States, an analysis from five counties in Georgia found that superspreading appeared to be “widespread across space and time,” and that 2 percent of the infected seeded 20 percent of the cases.
Most of these events took place in coronavirus hot spots of which most people are now aware: buildings where people live in close quarters, such as nursing homes, prisons, worker dormitories and cruise ships. There have been a fair number of clusters at meat-processing and frozen food factories, as well as at a curling event in Edmonton, Canada, leading some to speculate that temperatures could be a factor. (...)
As of Friday, she was staring at a spreadsheet with 187 infected at Harper’s Restaurant and Brew Pub.
“The tables were six feet apart, but no one stayed there,” she said. “The DJ was playing music so people were shouting, the dance floor started to get crowded. We had flattened the curve and then boom.”
The East Lansing case is what’s known as a superspreading event — possibly the largest so far in the United States among the general public. Many scientists say such infection bursts — probably sparked by a single, highly infectious individual who may show no signs of illness and unwittingly share an enclosed space with many others — are driving the pandemic. They worry these cases, rather than routine transmission between one infected person and, say, two or three close contacts, are propelling case counts out of control.
More than 1,000 suspected clusters — ranging from the single digits to thousands — have been logged in a database compiled by a coder in the Netherlands. A megachurch in South Korea. A political rally in Madrid. An engagement party in Rio de Janeiro. Nearly all took place indoors, or in indoor-outdoor spaces.
Even as the Trump administration pressures schools to reopen this fall, the latest research suggests that understanding how and why these events occur — and how to prevent them — is key to reopening safely. In recent days, governors from at least 18 states, including Michigan, have backtracked on plans to loosen restrictions due to outbreaks.
But even those efforts may fail if people ignore the most common ways the virus is considered to spread. Transmission, it turns out, is far more idiosyncratic than previously understood. Scientists say they believe it is dependent on such factors as an individual’s infectivity, which can vary person to person by billions of virus particles, whether the particles are contained in large droplets that fall to the ground or in fine vapor that can float much further, and how much the air in a particular space circulates.
Donald Milton, a professor of environmental health at the University of Maryland, and other experts have wondered if superspreading events could be the “Achilles’ heel” of the virus. If we could pinpoint the conditions under which these clusters occur, Milton argued, we could lower the transmission rate enough to extinguish the spread.
“If you could stop these events, you could stop the pandemic,” Milton said. “You would crush the curve.” (...)
As we enter the seventh month of the global pandemic, scientists are still frustratingly in the dark when it comes to key aspects of how the virus is transmitted.
Why, for instance, didn’t the earliest infections in the United States, or the infamous Lake of the Ozarks party, spur lots of cases, while a much smaller gathering at a Michigan bar produced nearly 200? Why out of countless large gatherings held — church services, soccer games, choir rehearsals, and Zumba classes — did only a fraction ignite significant infections?
Part of the uneven spread of the coronavirus — and the phenomenon of superspreading — can be explained by extreme individual variation in infectivity, researchers say.
Some people will not transmit the virus to anyone, contact tracing has shown, while others appear to spread the virus with great efficiency. Overall, researchers have estimated in recent studies that some 10 to 20 percent of the infected may be responsible for 80 percent of all cases. (...)
A growing body of evidence suggests that SARS-CoV2, like other coronaviruses, expands in a community in fits and starts, rather than more evenly over space and time. Adam Kucharski of the London School of Hygiene and Tropical Medicine has estimated that the value of what’s known as the k-parameter — a measure of how much a virus tends to cluster — indicates that just 10 percent of people may be responsible for 80 percent of novel coronavirus cases.
Real world data corroborates the skewed transmission pattern.
In a detailed analysis of outbreaks in Hong Kong, for example, researchers found three distinct groups of incidents. The superspreading individuals, representing 20 percent of the total, were responsible for 80 percent of transmissions. A second group, involving about 10 percent of cases, transmitted the virus to one or two others. The final group, 70 percent, did not infect anyone else at all.
In Israel, investigators looking at 212 cases concluded that they could be linked back to 1 to 10 percent of people. And in an outbreak in a South Korea office tower, investigators found that about 45 percent of 216 workers got the virus from a single person. In the United States, an analysis from five counties in Georgia found that superspreading appeared to be “widespread across space and time,” and that 2 percent of the infected seeded 20 percent of the cases.
Most of these events took place in coronavirus hot spots of which most people are now aware: buildings where people live in close quarters, such as nursing homes, prisons, worker dormitories and cruise ships. There have been a fair number of clusters at meat-processing and frozen food factories, as well as at a curling event in Edmonton, Canada, leading some to speculate that temperatures could be a factor. (...)
The rest of the known superspreading events were set in a hodgepodge of social venues where people gather in crowds: concerts, sports games, weddings, funerals, churches, political rallies, restaurants, shopping centers. And nearly all took place indoors, or in venues with indoor-outdoor spaces.
by Ariana Eunjung Cha, Washington Post | Read more:
