Poop can reveal a lot about a person’s health. It contains all kinds of things that leave the body, such as fiber, excess fluids, and live and dead bacteria. And when a person is sick, they can also shed fragments of a virus that they may be carrying, even when they are not yet showing symptoms.
This means that before people are diagnosed with a virus, traces of it can be collected from sewage systems.
For decades, scientists have used this knowledge and tapped into wastewater to monitor things like polio and E coli.
And now, researchers and scientists are monitoring sewage systems around the world to track exposure to SARS-CoV-2, which is the virus that causes COVID-19.
In Unalaska, Karie Holtermann, laboratory manager at the island’s wastewater treatment plant, began testing sewage water to track the virus last July. And for months it worked really well, helping the city identify outbreaks and learn more about exposure to COVID-19. But now, as vaccinations increase and the delta variant becomes more prevalent, Holtermann says she finds inconsistencies in the data, making it more difficult to track the number of local cases in the water.
“[The wastewater testing] is able to predict a peak, ”said Holtermann. “Basically he can choose [the virus] before clinical cases start to arrive. So if the virus is widespread on the island, we will see it in the sewage.
Here’s how the tests work: First, she said, she gets a water sample from the island’s “tributary”, which is basically the entire island’s sewer. From there, she extracts the RNA and throws it into a quantitative PCR machine, which tells her how much COVID is floating in the community.
Because it can help warn of outbreaks, she said, the data is meant to be an additional tool for the city. According to Holtermann, peaks in COVID found during water sampling will appear between a few days and a week before being detected during testing.
On a recent weekday afternoon at the treatment plant, she pulled a graph of the island’s viral loads in sewage and gestured to a February data point.
“This spike that happened here – it really followed the number of people who entered the clinic at that time,” Holtermann said.
Part of the reason the datasets correlated so well, she said, is that very few people were fully vaccinated and all but a few cases during that February peak. were related to industry.
Local seafood processing factories require strict testing for all of their employees and have previously mandated anyone coming to work from outside the island to isolate and get tested. This means that most of the positive cases were tracked and recorded by the city through test data and also appeared in sewage. The data points matched almost perfectly.
Holtermann then moved his finger across the screen, further down on the graph, and pointed to another more recent spike in viral load found in the city’s sewage from late August. But data from positive COVID tests showed a smaller increase.
“So this time when it got this far, there were probably a lot of people around and they just weren’t going to get tested,” she said.
Differences between wastewater data and test results are increasingly common on the island.
Wastewater samples taken in late August, for example, show viral loads only about 25% lower than they were in February, when the number of cases skyrocketed to nearly 200. But the number The city’s total cases during the August sewage peak only reached a peak of around 30.
“When we had the peaks, it didn’t necessarily match the number of people going to the clinic, but that’s probably because now it’s in the community and people are vaccinated, and they don’t necessarily go. get tested, ”said Holtermann.
There are a few factors that could contribute to the inconsistencies between the two data sets, she said. People with the delta variant may shed more of the virus. In addition, fishing vessels sometimes discharge their sewage at the island’s sewage treatment plant, and those on board could be infected with the virus. If so, they would also throw fragments of it down the toilet, which could then appear when Holtermann takes samples of the wastewater. But infections would not appear in the city’s case count, as these fishermen are likely not being tested locally.
But Holtermann said it is much more likely that there are many more people in the community with the virus who have never been tested. In other words, she said the virus was likely more widespread than the city’s tests show.
“The higher the viral load, the more prevalent it is in our community,” said Holtermann.
Because variables – like the exact amount of virus transmitted by people with the delta variant – make estimating numbers tricky, she wouldn’t say exactly how many people on the island she said likely had the virus on them. the basis of recent peaks in sewage.
Unalaska City Manager Erin Reinders said there may be more people infected with the virus than the city’s testing data shows, but she believes the gap in the data is probably related to other variables.
“I think what is probably the most likely is that we have the delta variant, which is now present. [and] has a higher viral load than previous COVID-19 viruses, ”she said.
City officials learned of a first increase in local sewage around mid-August, after community members gathered for two events during one of the island’s busiest weekends since the start of the pandemic.
In light of this increase and new cases of virus acquired in the community, the city has moved into the high risk category, closing several of its municipal buildings and requiring masking in all indoor public places. While this virus spike in the city’s sewage has continued to climb, the city has not increased other protection measures and schools and most businesses have remained open.
Now, as both cases and wastewater levels of COVID-19 decline, the local risk factor changed to “moderate”.
The Centers for Disease Control and Prevention says the wastewater analysis data is not intended to replace existing COVID-19 surveillance systems. And Reinders said it was meant to be preventative – to help “supplement” the rest of the city’s data, rather than showing an exact number of positive cases.
“We see it as part of a body of information,” Reinders said. “So obviously you can’t determine how many cases we have with the [wastewater] results there. But that’s sort of another indicator to look at, to see if there are any trends that correlate with the number of cases. “
The city only started actively sharing wastewater data with the public at the end of August, when it released a online dashboard – which contains a graph of the viral load in the water and a graph showing the number of local cases.
Reinders said the city previously shared the information directly with the local clinic, but the dashboard is a chance for the public to see local COVID-19 information as well.
Although the dashboard does not contain a descriptive analysis of what the data means in the charts, according to Holtermann, the island’s wastewater figures look good. Data shows viral loads in wastewater are declining, as are the number of local cases.
She said she didn’t know what the data will look like in the future. As more people get vaccinated and new variants continue to emerge, it is likely that there will be inconsistencies between viral loads and the number of cases recorded.
Still, she said it’s important to stay one step ahead, especially when the nearest hospital is around 800 air miles away.
Holtermann shared the island’s COVID-19 data with researchers across the country earlier this summer in the US Department of Homeland Security Virtual Wastewater Monitoring Workshop.
She said the workshop provided an opportunity to collaborate with other cities, universities and health organizations to standardize methods so that they can collaborate more easily in the future – whether with COVID surveillance – 19 or to monitor things like foodborne illness.
Holtermann said she would soon begin testing wastewater samples from the nearby island of St. Paul. These samples will be flown to Unalaska every week.