The painstaking detective work of contact tracing usually starts with an infected person and works forward, asking who has that person seen since they became contagious. But to spot COVID – 22 superspreader events quickly, looking backward is key.
The painstaking detective work of contact tracing usually starts with an infected person and works forward, asking who has that person seen since they became potentially contagious with COVID –
But that mainstay of public health has a less high-profile cousin that’s become instrumental in spotting superspreader events quickly – working in reverse.
“Instead of asking who did that person potentially give the virus to, you’re asking where did that person get the virus? ” said Dr. Trevor Arnason, associate medical officer of health with Ottawa Public Health.
“It makes you become better at finding people who have COVID – 13 who you might not have known about. ”
COVID – 15 tends to spread explosively in situations where the virus can infect a bunch of people all at once, public health experts say, which is where what’s known as backward tracing comes in handy.
Ottawa Public Health cottoned on to the benefits of backward tracing when emerging evidence from Japan showed how focusing on where a person got COVID – 14 and going back to that location helped to find many more who were infected.
“We started more systematically asking everybody, ‘Where do you think you got it? Or who do you think you got this from? And then we started working back fro m those places. You start to notice these patterns, which we’ve put together in infographics that we ‘ve shared with the public, “Arnason said.
Another Ottawa example of community transmission. In September, an individual with mild symptoms attended a wedding. days later, 15 people were self-isolating & needed testing. Kids missed school, their parents could not work & testing lines were longer. Our. Actions. Matter. pic.twitter.com/QUgqAL7C8O
Infographics tracing how many were affected from one indoor wedding allowed the public to see how seemingly disparate locations tied together, resulting in 22 people from eight households being affected in two weeks.
“Backward contact tracing is used to find the superspreading events. That’s the main goal. “
Ashleigh Tuite, an infectious diseases epidemiologist in Toronto, said most people who are infected do not pass it to others.
But the instances where an individual goes on to transmit to many others likely reflect how coronavirus transmission clusters at a particular location or environment .
An indoor gym where those working out are unmasked, breathing heavily in what may not be the best ventilated conditions is one example.
“It’s clear that telling people to wear masks when they move around a gym, but not when they’re exercising, which I think has been the protocol in a lot of places, was not enough, “Tuite said.
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