Fresh projections suggest that 1,100 people in Washington state have been infected with the SARS-CoV-2 coronavirus, and that the outbreak could be due for a rapid rise. What to do about it? One piece of advice is to distance yourself from others — and data gathered during last year’s “Snowpocalypse” provides evidence that the strategy works.
The potential risk, and the potential remedy, came into the spotlight today thanks to comments made by Washington Gov. Jay Inslee as well as by researchers who are using the Seattle Flu Study to track the spread of coronavirus.
During an Olympia news briefing, Inslee said the math behind the outbreak’s doubling effect looks “very disturbing.”
“If there are a thousand people infected today, in seven or eight weeks there could be 64,000 people in the state of Washington, if we don’t somehow slow down this epidemic,” he said. “And the next week it’d be 120,000, and the next week it’d be a quarter-million.”
As disturbing as it sounds, Inslee’s description of the current trend parallels what Trevor Bedford, an epidemiologist at Seattle’s Fred Hutchinson Cancer Research Center, said in his latest Twitter thread about the spread of COVID-19 disease.
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Bedford and other researchers are working with figures gathered by the Seattle Flu Study, a group that’s been using samples collected in a variety of settings to monitor the spread of infectious diseases, including influenza and coronavirus.
One of Bedford’s colleagues is Michael Famulare, principal research scientist at the Institute for Disease Modeling in Bellevue, Wash. Famulare’s computer simulations put the current number of active coronavirus infections in the Seattle area at 1,100 (with a 90% uncertainty interval between 210 and 2,800 infections).
As of today, Seattle-King County Public Health is reporting 190 confirmed cases, and the statewide tally is 267 cases. That’s far fewer than the simulations suggest. Bedford and other epidemiologists explain the disparity by saying that most of the people with the virus haven’t yet been able to take a test, or their symptoms are so mild that they don’t even bother to seek testing. Nevertheless, they’re able to pass along the virus due to a phenomenon called “cryptic transmission.”
Based on the tracking to date, it appears to take six days for the number of infections to double. That rate squares with the concerns that Inslee voiced today, and with concerns that Bedford voiced about a “growing outbreak” in the Seattle area. “If steps are not taken to increase social distancing … I fully expect cases to keep climbing,” Bedford wrote.
In addition to frequent hand washing and other hygienic measures, the strategy of social distancing — that is, avoiding crowds, particularly if you’re sick or at high risk due to age or underlying illness — ranks among the top tips for slowing down the epidemic. But is there evidence to support that strategy?
Coincidentally, one of the latest lines of evidence comes from Bedford, Famulare and fellow investigators from the Seattle Flu Study, in the form of a paper posted to the MedRxiv preprint server. Their findings are based on what happened in February 2019, when much of the Seattle area was snowed in by a heavy blizzard.
Last year’s Snowpocalypse caused a lot of involuntary social distancing, and that provided an opportunity to study the effect on the spread of viral infections. The coronavirus that causes COVID-19 wasn’t on the tracking list, since it didn’t exist back then — but a different strain of coronavirus was, along with several flu strains.
The data collected through the Seattle Flu Survey found that the weeklong stretch of school closures, impassable roads and event cancellations dampened the expected infection rate to a degree ranging from 3 percent to 9 percent, depending on the virus. What’s more, the dampening effect seemed to be strongest for viral outbreaks that were just about to reach their peak.
The study authors argue that social distancing doesn’t need to last for months and months — which is likely to come as good news for Seattleites who are settling in for a social freeze-out. Last year’s Snowpocalypse demonstrated the effect of “a more realistic, high-intensity, short-duration social distancing intervention, where schools and workplaces are closed and re-congregation is discouraged for approximately two weeks,” the researchers wrote.
“Our study suggests that such an intervention could be beneficial in reducing the total incidence if implemented near the peak of a pandemic,” they said.
Could it all be over by April? That seems unlikely, based on what China and Italy have been going through. But in the midst of a pandemic, pretending that you’re stuck in a blizzard might at least make social distancing seem more palatable.
In addition to Bedford and Famulare, the co-authors of the preprint paper, “Effects of Weather-Related Social Distancing on City-Scale Transmission of Respiratory Viruses,” include Michael Jackson, Gregory Hart, Denise McCulloch, Amanda Adler, Elisabeth Brandstetter, Kairsten Fay, Peter Han, Kirsten Lacombe, Jover Lee, Thomas Sibley, Deborah Nickerson, Mark Rieder, Lea Starita, Janet Englund, Helen Chu and the Seattle Flu Study investigators. The paper has not yet been evaluated through peer review, and so should not be used to guide clinical practice.
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