Wastewater monitoring can accurately assess the spread of disease
New coronavirus cases reported in the state of North Carolina have reached their highest number since winter, but the reported number still does not reflect the level of coronavirus found in sewage.
COVID transmission could rise again as cities across North Carolina — regardless of their level of community spread — haven’t pushed public masking like they did in the winter.
As a next and perhaps more effective step in helping individuals make personal protection decisions, the government could transform wastewater monitoring into local risk prediction, according to researchers at the University of North Carolina who lead NC wastewater studies.
UNC microbiologist Rachel Noble has been working on sewage COVID testing since early 2020. Her lab collaborates with other academics, the state Department of Health and Human Services, and state services. sewage utilities to create the COVID surveillance framework.
The NCDHHS revised its COVID severity measure earlier this year by elevating the sewage measure to one of the primary factors. Wastewater data is updated every Wednesday on the DHHS dashboard.
About 25 wastewater treatment utilities are now collecting and testing for coronavirus concentration in NC’s more than 100 sewer systems. Noble’s lab tested the majority of the wastewater samples and provided data for DHHS.
The sewage test for viruses and pathogens is designed to reflect the full extent of community disease. Infected people, even those with mild or no symptoms, shed the virus in sewage, which is collected for laboratory analysis.
COVID-19 wastewater monitoring was originally used to detect outbreaks before clinical findings. As testing and reporting dwindles due to a lack of funding or public fatigue hiding from COVID, sewage monitoring may become what people can use to determine daily risk levels.
Similar to the severe thunderstorm warning system, disease risk categories could help people decide how to protect themselves when their locality is threatened by disease outbreaks with much quicker warning.
The alert could include regional recommendations and be broadcast through TV and radio stations, regional newspapers and mobile phone apps.
“Not everyone can look at a chart [on the website] and understand what is happening. We need a way to interpret it for the public so they can understand the risk to their daily lives,” Noble said.
The concept of disease risk categories from sewage viruses has not been pursued for very long and will require effort from researchers to develop, she added.
Divergent virus waves
DHHS continues to record and report positive COVID-19 tests while recognizing that the number does not reflect the full extent of the disease’s spread in the community. The current community-level calculation using the number of cases underestimates transmission.
The number of coronaviruses in sewage has increased in some cities, but this trend has not been reflected in clinical reports.
“Missing” infections take many forms, including the prevalence of home testing that is not reported to DHHS.
Tourists can also contribute to the gap. They may shed the virus during their visits but not get sick or test positive before returning home.
Cities with airports like Charlotte and Raleigh, where passengers fly in and out, may also see an increase in viruses in sewage that isn’t always reflected in case reports.
Virus count in wastewater
Data from DHHS shows that the recent surge was largely caused by the omicron BA.5 subvariant. The variant has a very strong transmission capacity that breaks down protection from vaccines and boosters, and previous immunity against COVID infection.
No matter how severe the symptoms of COVID are, when a person uses water and flushes it down the toilet, the viral material travels to the sewage treatment plant. The trip only takes a few hours to less than a day.
Wastewater utilities could collect untreated sewage for 24 hours, which would accurately capture the daily activities of the community. Noble’s lab can complete the COVID particle count typically within a day of receiving the wastewater samples.
Researchers can also use these tests to detect many other future pathogens, including still-emerging COVID variants and the recent spread of monkeypox.
“We are able to monitor monkeypox and the state has asked us to do the testing,” Noble said.
They have not detected any monkeypox DNA in the sewage samples for the past two weeks. It is not known how many cases must occur in a given area before detection in sewage is possible.
Noble’s lab receives tons of bottles filled with dirty water every week from more than 20 wastewater treatment plants across North Carolina. Each bottle represents a population ranging from a few thousand in Beaufort to hundreds of thousands in one of the factories in Raleigh.
At the end of July, Noble’s team worked intensively in their laboratory in Morehead City to test and analyze wastewater for 80 consecutive weeks.
Noble said sewage monitoring will be more useful in areas where medical facilities are scarce. Her team has expanded the number of plant locations in recent years to include more rural areas, and she hopes to continue to expand the wastewater monitoring service.
“If the medical facilities are not as numerous for the population, they will not be tested. And if they are not tested, they will not be reported as positive cases,” she said.
Noble’s team also works with DHHS and the CDC, teaching them how to translate the data for everyday use.
“We try to work with them to create more [relevant] public information,” she said.