The university switched to the batch testing in October involving four saliva samples being tested together for COVID-19. At the same time, COVID cases began spiking on campus.
Will Laegreid, Director of the State Vet Lab and overseer of the COVID surveillance testing at the university, said, “It doesn’t have anything to do with the pooled testing. We don’t report those out to the state.”
The university reported 1,970 positive cases in 2020, most of which were in the fall. Cases are now much lower, at only 175 cases reported in 2021. The test positivity rate is now 0.2%.
Laegreid said surveillance testing is just that, surveillance. If someone is in a group that tests positive, they have to retest individually using a diagnostic test. Likewise, if you’re in a pool where all people test negative, those are not counted towards the county test positivity rate.
Only those diagnostic positive tests, taken through Vault or through the state, are actually counted in the statistics.
“Our numbers do look higher because we are testing more and we are finding more positive cases. If you don’t look you’re not going to find them,” Laegreid said.
Eliot Hegy, assistant supervisor of all UW testing, said he suspects cases were high in the fall for other reasons.
“Fall is the beginning of flu season, so immune systems might be taxed from fighting more than one illness,” Hegy said. “And more people get sick as the weather gets colder.”
Hegy said students returning to campus meant more interactions and more cases. After enough people had been infected, and therefore became immune, cases fell significantly. This may be the reason for such low cases during the spring semester, in addition to mass vaccination efforts.
“The testing method explains none of this decrease as both tests were highly accurate and administered at the same weekly rate to faculty, staff and students,” Hegy said.
The switch from diagnostic to surveillance testing in October, and the coinciding spike in COVID cases is likely just a coincidence, Hegy suggested.
Laegreid said, “We are testing lots and lots of people, most of whom are unlikely to be positive, which means we are going to find more cases than in a community that only tests when someone comes in sick.”
“It is the asymptomatic patients that are going out and spreading the virus,” Laegreid said. “That’s who we are trying to detect.”
