Oregon sewage data shows far more people have contracted COVID than tests indicate

Last month, a new COVID-19 variant from the Omicron family spread across Oregon, causing a seventh wave of infections.

On paper, this seventh wave didn’t look particularly impressive, peaking in late May with about 1,500 new cases reported per day. But data from wastewater samples collected at treatment plants across the state suggests the BA2-Omicron variant is quietly causing far more infections than state testing numbers show.

“Sewage across the state is more or less at or near record highs,” said Tyler Radniecki, associate professor of environmental engineering who leads the research effort on wastewater sampling at Oregon State University.

The OSU project is part of a nationwide COVID-19 wastewater monitoring program. Virus levels in Oregon during the current surge are similar to what the team saw during the peaks of last August’s delta rise and January’s first omicron rise.

By the end of May, virus levels in sewage samples were being recorded as “heavy,” indicating a significant outbreak across much of the state. Virus levels were even higher in a handful of communities, including Forest Grove and Bend, indicating particularly intense BA2 outbreaks.

What the effluent shows, Radniecki says, is that the state’s number of COVID-19 cases is a very significant underestimate of the true spread of BA2.

However, the wastewater monitoring does not provide any information about how badly a certain variant causes illness. Hospitalization data shows that BA2, like other Omicron variants, mainly causes milder cases, despite the number of people in intensive care with COVID-19 rising to over 50 this week.

Case numbers have always been a very imprecise measure of actual infections because they depend heavily on the number of people being clinically tested for COVID-19. And as more people use rapid tests at home, the number of clinical tests is declining, making case numbers an even less reliable indicator of the spread of COVID-19.

To better understand how prevalent the virus is, some local health authorities are increasingly relying on sewage data instead.

The surveillance method takes advantage of the fact that many people infected with COVID-19 shed the virus in their feces. The OSU team collects data from about 40 treatment plants across the state, from Ontario to Warm Springs to Florence.

The sewage treatment plants collect a representative sample of the inflowing wastewater over a period of 24 hours via a small filter every week. The filters are rolled up, put into tubes and shipped to Corvallis. OSU scientists identify and quantify viral RNA on the droplets in the filters. After two years of refining the process, it now takes about 4 to 5 days from when a sample is taken to when OSU has an estimate of how much COVID-19 virus is in it.

The researchers are also extracting genomic sequences from the wastewater samples to look for variants of concern.

George Conway, Deschutes County Health Supervisor, says two things make wastewater monitoring powerful. First, everyone who lives above the treatment plant contributes to the sample.

“That’s a common source,” Conway said. “This helps us better assess the current rate of infection in the community.”

Second, people infected with COVID-19 begin to shed the virus in their feces before they are symptomatic and before they decide to get tested. As the OSU team has streamlined its protocol, the effluent is getting closer to its goal of providing a real-time view of outbreaks as they develop.

“It gave us reliable early warning,” Conway said of the testing. “That can inform our communications with medically vulnerable individuals and give medical providers and hospitals time to better prepare for an increasing caseload.”

The wastewater test data is publicly available. Radniecki encourages people to watch it to understand if the virus is spreading or receding in their community.

“When you see very big signals in your community, it can change your behavior or the level of risk you’re willing to take,” he said

Right now, for example, data shows that COVID-19 concentrations are leveling off or decreasing in most parts of the state, but are rising in parts of southern Oregon.

Reading out the data requires some work. Each colored dot represents a single community. Click on it and a chart will appear showing how the concentration of the virus in that community has changed over time. The graph uses a logarithmic scale to show levels of virus. Similar to how we measure the magnitude of earthquakes, this means that a small increase in the value at the high end of the scale represents a large increase in virus levels in a community’s wastewater.

Next month, Eugene and Springfield will host the World Athletics Championships, an international athletics competition and one of the world’s largest sporting events. The poop in these cities, Radniecki said, is especially worth seeing from July 15-24, when track and field athletes from all over the world will be in town. It will be a good place to look for new COVID-19 variants and a unique opportunity to study how a massive sporting event is affecting public health.

Copyright 2022 Oregon Public Broadcasting. To see more, visit Oregon Public Broadcasting.

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