Superspreading’ events, triggered by people who may not even know they are infected, propel coronavirus pandemic

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Sun, 2020-07-19 11:55 — mike kraft

‘Superspreading’ events, triggered by people who may not even know they are infected, propel coronavirus pandemic Most spread the virus to only a few people — or none at all. But a small percentage transmit it with alarming efficiency, studies show. Ariana Eunjung Cha Washington Post

Most spread the virus to only a few people — or none at all. But studies show a small percentage transmit it with alarming efficiency.

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 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.

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