Genetic Testing Results for Swan and Delaware Creek E. Coli

On August 25, the City of Toledo worked with Microbial Insights to conduct DNA-based analysis to determine whether elevated E. coli levels were coming from human sewage or from natural sources like wildlife. We did this testing because even after sewer overflows into the waterways stopped, E. coli levels remained elevated.

The genetic testing looks for a DNA marker that is found in human gut bacteria, but not in E. coli. Its presence in the water helps us assess how likely the E. coli in the water is due to human waste.

The results showed that in Swan Creek and Heilman Ditch, there’s a very low probability the E. coli is the result of sewer overflows and is most likely from animals like deer or geese.

Delaware Creek, however, showed a moderate probability of sewage influence. Since we have no evidence of an active overflow, this could be attributed to soil contaminated by previous overflows being washed into the creek when it rains. The genetic testing doesn’t tell us whether the bacteria is alive or dead, just that the DNA remains. A few good rainstorms and a little more time should let nature flush the area.

Regardless of the source, exposure to E. coli can be harmful and the public health advisories for both creeks remain in place. We are continuing to see reductions in our weekly testing as the weather starts to turn colder.