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Covid Early Warning Signal - Sewage

Last updated on August 10, 2020 07:37 pm

Every time we flush our toilets, we help regional and state officials understand the state of Covid-19 in eastern Massachusetts.

If we’re connected to MWRA sewage, that is.

That’s because wastewater tests can offer an early look at pandemic trends.

“People infected with SARS-CoV-2 shed the virus in their stool even before they show symptoms of Covid-19,” according to an article at the medical news site Stat co-authored by Ashish Jha, director of the Harvard Global Health Institute and professor of global health at the Harvard T.H. Chan School of Public Health.

“Analyzing sewage for the virus, using methods like the ones used for testing individuals, can predict the community level of infection one week to two weeks in advance of clinical diagnoses, and show increasing and decreasing levels of coronavirus infection and transmission.”

The MWRA has launched a pilot program with Biobot Analytics to test regional sewage three times a week, And, they publish results of Covid-19 levels detected.

That helps overcome a major limitation of Covid-19 molecular tests: Unless we test massive numbers of people very frequently and get results back quickly, those individual tests only give an incomplete picture of the situation days or even weeks ago.

Wastewater tests can’t serve as a replacement for testing individuals, since looking at regional sewage can’t help quarantine specific people or trace clusters and outbreaks. However, even without understanding what the “RNA copies per mL” is measuring exactly, we laypeople can see trends in the wastewater testing graph below:

MWRA 3-Sample Average of Covid-19 Detected in Wastewater

Test data from Biobot Analytics via MWRA, samples taken 3 times per week

“Testing sewage for polio virus was an important way to confirm areas polio-free, or to point to rising risk,” tweeted epidemiologist Dr. Lary Brilliant, who worked at WHO in the 1970s to help eradicate smallpox. “Some places like Boston are doing the same for #COVID virus fragments from human feces. It is an inexpensive simple monitoring tool that should be used everywhere.”

In addition to a summary aggregating all samples, MWRA splits data into North and South regions. There’s a somewhat-difficult-to-read map of the regions here. Framingham is in the South region, along with Ashland, Newton, Boston, and Braintree, among others.

The graph below shows data by region. You can click a region on the legend at right (you may need to scroll the page to the right in order to see the legend).

Finally, if you want a truly early look at trends, below is a graph of each sample instead of a three-sample moving average. View it with the understanding that there could be unusual fluctuations in one particular sample. Again, you can click on a region in the legend at right to turn it off or on in the graph.

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