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Example 3: Retrospective ("backward") vs. prospective ("forward") contact tracing.
Lots of interest in backward contact tracing after @zeynep's article!
#1 tests positive. You interview her and she tells you the exact date her symptoms started. 1/
https://twitter.com/zeynep/status/1311329981419728898?s=20
Lots of interest in backward contact tracing after @zeynep's article!
#1 tests positive. You interview her and she tells you the exact date her symptoms started. 1/
https://twitter.com/zeynep/status/1311329981419728898?s=20
Following protocol, you interview her about everyone she met starting 2 days before the date her symptoms started. Family members are usually obvious. She lives with her brother and sister, parents and grandmother. Also another brother that lives at a different address. 2/
She's a waitress so you call her boss at the restaurant. He's already closed it and told all of the staff to get tested. He and another employee end up testing positive (no symptoms!).
So you've called 11 close contacts and found 2 cases!
Nice job with the forward tracing. 3/
So you've called 11 close contacts and found 2 cases!
Nice job with the forward tracing. 3/
But now it's time to go backwards.
The goal of forward tracing is to warn anyone who she might have infected. People can be infectious 2 days before symptoms start.
But how did she get infected? To figure that out, you have to go further back than 2 days. 4/
The goal of forward tracing is to warn anyone who she might have infected. People can be infectious 2 days before symptoms start.
But how did she get infected? To figure that out, you have to go further back than 2 days. 4/
Did she get infected at the restaurant? It's possible, but that's not what she thinks.
4 days before her symptoms started she hung out with 4 of her closest friends.
#7 was the first to get tested, and she called everyone. In the end, every single one tested positive. 5/
4 days before her symptoms started she hung out with 4 of her closest friends.
#7 was the first to get tested, and she called everyone. In the end, every single one tested positive. 5/
Backward tracing often leads to forward tracing. #6 and #7 are sisters—their parents end up getting infected. 6/
But you can backward trace this group too!
True, they might have gotten infected at the gathering. But if you ask them, that's not what they think.
3 days before the gathering, #5, 6 and 7 attended a wake. And now you've got a lot more forward tracing to do. 7/
True, they might have gotten infected at the gathering. But if you ask them, that's not what they think.
3 days before the gathering, #5, 6 and 7 attended a wake. And now you've got a lot more forward tracing to do. 7/
"Why is it important to know where she got infected? You can't go back in time and prevent it from happening."
Backward tracing leads to forward tracing.
Going backwards leads to clusters, and testing and tracing clusters is a very high yield activity. 8/
Backward tracing leads to forward tracing.
Going backwards leads to clusters, and testing and tracing clusters is a very high yield activity. 8/
It also provides actionable intelligence.
If you detect an outbreak in a certain location (like a workplace), you can quash it if you act rapidly.
And if you see repeated clusters at the same types of locations, you can implement policies to stop them from happening. 9/
If you detect an outbreak in a certain location (like a workplace), you can quash it if you act rapidly.
And if you see repeated clusters at the same types of locations, you can implement policies to stop them from happening. 9/
"Isn't this obvious? Why doesn't everyone do backward tracing?"
It wasn't obvious to me. WHO and CDC protocols stress forward contact tracing. Backward tracing isn't part of standard protocol.
When we started doing this, it was mind blowing. 10/
It wasn't obvious to me. WHO and CDC protocols stress forward contact tracing. Backward tracing isn't part of standard protocol.
When we started doing this, it was mind blowing. 10/
"How can we learn backward contact tracing and cluster investigation?"
Not by adding a couple of new variables to your CRM!
This data is already in the heads of the contact tracers, collected during hours of interviews with cases and contacts. You just have to get it out. 11/
Not by adding a couple of new variables to your CRM!
This data is already in the heads of the contact tracers, collected during hours of interviews with cases and contacts. You just have to get it out. 11/
For starters, the Japanese Ministry of Health has posted this excellent slide deck. I'm sure that Hitoshi Oshitani would be happy to give you pointers (he did for us).
And the moral of the story...always listen to @nataliexdean
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https://www.mhlw.go.jp/content/10900000/000635891.pdf
And the moral of the story...always listen to @nataliexdean
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https://www.mhlw.go.jp/content/10900000/000635891.pdf
