COVID is primarily spread through the air, but infected people also excrete virus when they use the bathroom.
By testing sewage going to water treatment plants, it’s possible to get an idea of how much virus is being shed. More virus in wastewater means more infected people -- even before cases increase.
Researchers say more and more sewage systems in the U.S. are detecting increased levels of coronavirus recently.
The CDC said nearly 40% of wastewater sampling sites reported at least some level of increase over the past 15 days.
Wastewater data cannot estimate the number of cases in a community, but monitoring that kind of data can serve as an early warning sign of increased transmission. It often detects increasing infection days before positive case counts.
There are more than 400 wastewater testing sites scattered across Michigan. However, attention is focused on 20 sewershed sites in 18 counties and the City of Detroit. They make up the Sentinel Wastewater Epidemiology Evaluation Project (SWEEP).
You can see that the trend in the 15 days generally preceding March 3 showed a decrease in 12 of the 20 testing sites. However, in the Metro Detroit area, particularly the Great Lakes Water Authority Detroit River, Oakland, Macomb and Wayne county sites -- the 15-day trend is flat. Not decreasing.
Read: Complete Michigan COVID coverage