NCW — Mass COVID-19 testing in communities across Chelan and Douglas counties since mid-August found 77 positive cases out of 4,500 tests conducted, a 1.7% positive case count rate.
The positive case rate has been around the 1% mark consistently since September, according to a Chelan-Douglas Health District news release. Except for one outbreak in Leavenworth the health district identified where it jumped to 3.4%.
The 1.7% rate is about where the statewide average is likely at, said Dr. Peter Houck, a Chelan-Douglas Health District epidemiologist. But people should be careful drawing conclusions using this data, Houck said, as the 13 community mass testing wasn’t meant to estimate the percentage of people with the virus.
“The real reason is to find as many people, who are infected. Isolate them so they don’t transmit the infection to other people. Find their contacts, quarantine their contacts to see if they develop disease. And keep any of the contacts who develop disease from spreading it to someone else,” Houck said. “That’s the real reason for doing the testing.”
The problem with the data from the mass testing events is it’s a convenience sample, he said. Health officials are testing anyone who shows up and is willing to get tested. They do not know if the people tested represent the population as a whole.
To accurately figure out the rate of infection in the community health officials would need to take a random sample, Houck said. They would need to randomly select households and ask them to get tested.
“That’s a convenient sample, because it’s easy to do, it’s not statistically representative and the problem you can have, if you are not careful, your convenience sample can give you wildly wrong numbers,” he said.
Health district officials are using the testing, though, to notice spikes that can identify outbreaks, Houck said.
The testing in Leavenworth from Sept. 8-11 revealed an outbreak in a packing house, according to the news release. Health district officials had people isolate and quarantine in response.
The community of Peshastin also appeared to have a rather large amount with a 7% positive rate, but that was because there were four positives out of only 53 tests, Houck said.
“I’m making this up again, but those four cases in Peshastin could have all been in one family and there could have been zero disease in the rest of the community,” Houck said.
The health district plans to continue testing communities throughout the two counties so people with the virus can isolate and health officials can trace the people they were in contact with, according to the news release.
Anyone aware of large areas where drive-through testing can occur can contact the health district at firstname.lastname@example.org.
People can also use that email to inquire about helping with testing by volunteering.