Tuesday, May 3, 2022
Transitions can be awkward. My second screen isn’t connected yet, so I’m doing research on my iPad and my laptop while writing the article on my new desktop. Hey, I just moved in. If this looks ugly, you should see my closet.
We’re in this kind of phase with COVID. We’re collecting data all over the place, but how reliable is it and how do we use it? This week there’s a new emphasis on wastewater. “Here we go again,” proclaimed this morning’s L.A. Times. “California coronavirus cases rising. Is a new wave coming?” And then in the Wall Street Journal: “COVID-19 Cases Rise in the U.S., With Limited Impact.” Both articles cite wastewater surveillance. We are going to see more of this. Ironically, the more available individual test kits are, the less useful they become for tracking community spread because home results are not reported to a public health agency. Enter the wastewater.
National wastewater surveillance for COVID-19 has been in use since September, 2020, when the CDC established the National Wastewater Surveillance System or NWSS. Although COVID-19 is not spread through feces like cholera, typhoid, hepatitis A, and many other diseases, the virus can be detected in feces. By taking periodic samples of sewage over time and testing for the coronavirus SARS-CoV-2, local health departments can send data to the NWSS date portal where the results can be analyzed, compared, and evaluated. You can see the results for individual “sewersheds” (sewage drainage areas) on the interactive map on the CDC website.
The sites were set up at different times and as you can see on this map, the testing sites are not evenly distributed. They do not represent uniform population sizes or city boundaries. Instead they represent the wastewater drainage collected from a geographical area.
For example, the District of Columbia Sewershed includes the counties of Fairfax, D.C., Prince Georges, Loudoun, and Montgomery, totaling a population of two million. Testing started on Jan. 25, 2022 and samples are taken every fifteen days. This graph shows the trends for the area as a whole from Jan. 25, 2022 to April 13, 2022:
The metrics on the CDC graph are relative, not absolute, with 100% being the highest concentration a site has ever registered. An example of a quantitative metric used for samples collected from Portland, Maine, which shows that the number of viral copies per liter of sewage has doubled in viral concentration since the samples collected 10 days ago.
Although the measurement in viral copies per liter of sewage cannot be translated to number of cases, the correlation can be demonstrated, as in this graph from Athens, Georgia, that I picked up on Twitter:
A major advantage of detecting COVID outbreaks through wastewater testing is its sensitivity. According to the Bio-Rad Wastewater Surveillance website, testing with the droplet digital PCR method can detect one case in a population of 10,000 and detect the first occurrence 6 days before testing. To learn more about the specific methods and capability of wastewater testing, refer to the Bio-Rad link below or search on “COVID wastewater testing laboratories”.
Wastewater drainage can be sampled upstream to monitor individual populations such as senior care centers, neighborhoods, college campuses, and prisons. COVID-19 tracking was to detect infections in college dormitories as early as the summer of 2020. It can detect the first appearance of COVID in a population before any symptoms appear and is completely independent of individual testing or asymptomatic cases. It can even detect the appearance and relative amounts of new variants.
Before signing off, I want to emphasize that wastewater surveillance is a worldwide project, as shown in the map below. I would love to investigate how it is being applied in other countries, but that is a topic for another day.
Wastewater viral load has been identified as a leading indicator, an early alarm system alerting epidemiologists to a viral threat long before lagging indicators such as hospitalizations and deaths. Although the relationship between wastewater metrics and other data such as cases and hospitalizations is still being worked out, these are the kind of epidemiological tools that will help us evaluate new virus crossovers in the future.
Today’s Notable Headlines
“North Carolina expands COVID-19 wastewater testing,” WRAL, May 2, 2022. https://www.wral.com/coronavirus/north-carolina-expands-covid-19-wastewater-testing/20261953/
“Portland wastewater testing shows sharp increase in coronavirus,” Portland Press Herald, April 29, 2022. https://www.pressherald.com/2022/04/29/maine-reports-470-new-covid-19-infections-friday/
“Wastewater helps find positive COVID-19 cases at UA dorm,” KOLD News 13, Aug. 27, 2020. https://www.kold.com/2020/08/27/wastewater-helps-find-positive-covid-cases-ua-dorm/
“NICD detects new Omicron sub-variant in wastewater in south western Johannesburg,” Cape Times, May 3, 2022. https://www.iol.co.za/capetimes/news/nicd-detects-new-omicron-sub-variant-in-wastewater-in-south-western-johannesburg-de919d12-7fd9-44af-9292-6d2e7ac1d91a
“National Wastewater Surveillance System (NWSS),” CDC, https://www.cdc.gov/healthywater/surveillance/wastewater-surveillance/wastewater-surveillance.html
“SARS-CoV-2 / COVID-19 Wastewater Testing,” BioRad, accessed May 3, 2022. https://www.bio-rad.com/en-us/feature/wastewater-surveillance-for-sars-cov-2.html
COVIDPoops19 Summary of Global SARS-CoV-2 Wastewater Monitoring Efforts by UC Merced Researchers, accessed May 3, 2022. https://www.arcgis.com/apps/dashboards/c778145ea5bb4daeb58d31afee389082
Why am I doing this?
The pandemic hit like a tsunami and the ripple effect will be felt for decades. World upheavals, deglobalization, housing shortages, the Great Resignation, supply chain disruptions–we’re navigating changes not entirely caused by the pandemic, but accelerated by it. Since March 11, 2020, this blog has examined the modern pandemic experience in the media and in everyday life, drawing on my experience as a medical technologist, a historian, and an ordinary person living through extraordinary times.