SCOTT SIMON, HOST:
There are no hard numbers for how many people in the United States are infected with the coronavirus. At Oregon State University, there is a new effort to arrive at those numbers, at least for one small city. NPR's Joe Palca has a report on the project known as TRACE.
JOE PALCA, BYLINE: TRACE has a straightforward goal.
BEN DALZIEL: To understand the prevalence of the virus in a community - in this case, Corvallis, Ore.
PALCA: That's Ben Dalziel. He's project leader. Prevalence means how many people have the virus at any given moment. Here's how TRACE works. Two-person teams go out on weekends, knocking on doors in different neighborhoods and asking residents to participate. If they agree, people take their own nasal swab, and the teams take the swab back to the lab for analysis. Participants can go online to get their results. They're also sent by mail. Each participating household gets a good-sized packet.
DALZIEL: There's a lot of forms. There's the quick-start instruction guide for collecting the self-collected nasal sample. There's leave-behind materials.
PALCA: During the week, Dalziel and his colleagues assemble all this stuff into kits. They then sort the kits into large plastic tubs based on who's going where.
DALZIEL: And then Saturday morning, down at the loading dock, there's, you know, rows and rows of team-based kits lined up, and vans start pulling up.
UNIDENTIFIED PERSON #1: Do you already have your bucket?
PALCA: This was the scene last weekend. Dalziel captured it for me on his smartphone. Each team grabs a tub...
UNIDENTIFIED PERSON #2: Team 6.
PALCA: ...And then gets last-minute instructions.
UNIDENTIFIED PERSON #3: Yeah, you're going to one census block today. It looks like it's in northwest Corvallis.
PALCA: It started raining, so teams hurried off to their vans.
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PALCA: Dalziel says the teams will be out again this weekend, and then one more weekend to complete the effort. Because of a shortage of tests, the Centers for Disease Control and Prevention has recommended that priority for testing go to people who are sick and might be infected with the virus, but that misses people who may be infected and spreading the virus but have no symptoms. TRACE tests people whether they're sick or not. Corvallis is a city of nearly 60,000 people. Dalziel says they don't need to test everyone to get a representative sample.
DALZIEL: The original proposal was 960 a weekend for four weekends.
PALCA: But they've scaled that back a bit. They now have preliminary results from the first weekend they were out, April 25 and 26.
DALZIEL: We had 237 households, and we tested 455 people.
PALCA: And how common was infection?
DALZIEL: The estimate is approximately 2 per thousand people, so 0.2%.
PALCA: Dalziel says that might not sound like much, but, remember; that was just a snapshot. It doesn't tell you how many people have been infected since the start of the outbreak. And it's also possible there are hot spots the team missed. Still, Dalziel says it's worrying.
DALZIEL: Two in a thousand is a sufficient level of prevalence that if we were to reopen too quickly, we would risk entering another epidemic exponential growth phase.
PALCA: Dalziel says expanded testing efforts like his project will be important to help officials know when it's safe to reopen a community and to catch flare-ups, should they occur.
Joe Palca, NPR News.
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