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There are only so many swabs you want to stick up your nose.
We’re into a third year of living with the COVID-19 pandemic, and a hefty, though unknown, number of people have been swabbed and tested for the novel coronavirus. In Virginia, local health districts report 13.4 million test encounters. That’s in a state of some 8.7 million residents.
We’re tired of dealing with COVID-19, and tired of testing. And yet COVID-19 infectivity numbers are steadily climbing in Virginia, with the state today reporting almost 2,018 new infections and a seven-day positivity rate of 8.7%. Rates were at 5.2% on April 10.
Fortunately, there are mitigating factors. Current COVID-19 variants seem less virulent, and many people have varying degrees of immunity from previous infections or from vaccination and boosting.
People are still testing, but many may use rapid, at-home tests and not report their results. Others may have mild symptoms and not bother to test, or they may be asymptomatic. Also, many hospitals and communities have moved away from asymptomatic programs, says Dr. Christopher Doern, director of microbiology and an associate professor of pathology for VCU Health. “That does hurt our ability to monitor community spread of the virus,” he says.
But, he notes, extensive testing continues, and we’re testing for COVID-19 at rates that exceed monitoring for any other disease or condition.
One monitoring tool that’s getting greater use and recognition is wastewater surveillance for COVID-19, testing wastewater at select treatment plants for the presence of viral RNA.
The viral RNA is shed by people who are infected through their feces. You can’t contract the novel coronavirus from the wastewater, and no patient contact is required to test it. It’s cheaper than other forms of testing, and it gives a broad perspective on rising or ebbing levels of the virus in a particular population. “It’s a nice way of broadly surveilling a population to look for changes and trends,” Doern says.
Virginia started a monitoring program in September 2021, according to Dr. Rekah Singh, the program manager for the Virginia Department of Health. It’s a sort of early warning system of what may lie ahead, as wastewater sampling will show virus shedding from people who are infected and have symptoms of COVID-19, and also people who are infected but who have yet to show symptoms of illness.
The U.S. Centers for Disease Control and Prevention say that such data can show an increase or drop in viral load trends four to six days before it’s reflected in clinical data.
“It’s a very useful leading indicator,” Singh says.
There are 25 participating wastewater treatment plants across the state. The commonwealth reports its data each week. You can see monitoring reports at the CDC website. Virginia is also working on its own dashboard, but that has not been activated for public access.
Think of the current wastewater surveillance program as offering a kind of screenshot of what’s happening in a community, an in-the-moment glimpse of infections in the entire pool; it does not allow for drilling down into a particular subdivision or building or a public institution such as a school, that would require closer-in, more specific testing at, say, a particular pump station.
It’s shown as a percent change in virus levels. Virus levels at sites show whether virus loads are higher or lower than past levels; a listing of 100% indicates activity that matches the all-time high, while 0% shows levels are at the lowest level recorded at a site. Site data is looked at for trends, whether levels are rising or abating.
Learn more about how the virus-level data is compiled.
It’s a useful tool, but there are limits to its utility. The CDC cautions that information from the monitoring program should be looked at as part of a larger data picture.
For example, it’s not indicative of the number of people who may be shedding virus in the community. There are also questions on such factors as how much virus is shed by individuals. Factors such as an influx of tourists or visitors, or rainfall in a watershed may impact virus levels in wastewater, as in systems serving many urban areas that also handle stormwater runoff.
Another caveat is the short time frame for the program, a bit more than 30 weeks. Utility will improve as the data grows.
Such variables also make it hard to compare numbers from the various facilities.
The data is useful in mapping trends. For example, Singh noted that it reflected the sharp increase in COVID-19 cases in the post-holiday surge, then caught the sudden, steep decline. By the end of February, 18 sites were reporting markedly low to undetectable levels of virus in the samples. By the end of March, viral loads were still low across the state. In the past few weeks, there’s been “a slow creep-up,” Singh says.
The data as of April 24 for the sewershed serving Richmond is showing relatively flat trendline for virusload.
Wastewater monitoring for disease is not a new idea, but it is gaining attention for its utility. It has previously been used in monitoring for diseases including polio and typhoid, and has also been used as a tool to gauge opioid use, according to Singh.
Wastewater surveillance is simple and relatively cheap compared with other surveillance methods, such as providing, processing and tracking results from COVID-19 tests for individuals. CDC grants are paying for the program in Virginia and other states. Singh says consideration is being given to making the pilot program permanent, and to expand it to include monitoring for other public health woes such as norovirus and food-borne illnesses.
“We can screen thousands and thousands of people with this,” Singh says. “It’s very cost-effective.”
