A new University of Colorado Boulder study revealed that there was leading source for airborne bacteria in the winter air above a few Midwestern cities—dog poop.

Rob Knight, a CIMB faculty member and associate professor in chemistry and biochemistry, was part of the team that measured the winter air quality in Chicago, Cleveland, Detroit and Mayville, Wisc. for airborne bacterial colonies.

They measured 100 air samples collected as part of a previous study by Colorado State University to determine bacteria components and levels. Cleveland and Detroit showed significant quantities of fecal bacteria in the atmosphere, with dogs being the most likely source. Chicago and small-town Mayville showed significantly less.

The research team analyzed the bacteria’s DNA in the collected air samples and compared what they found against a database of bacteria from known sources like leaves, soil, and human, cow and dog feces. They studied air quality in the winter because, with frozen ground and fewer plants, the bacteria from feces become more dominant.

Rob doesn’t know how impactful fecal bacteria from dogs are on human health. He says the team’s findings were unexpected and the study was not designed specifically to look at health effects. The team hopes to study more cities and map airborne bacteria across the nation.

The study was funded by the CIRES Innovative Research Program, the U.S. Environmental Protection Agency, the National Science Foundation, the Howard Hughes Medical Institute and the National Institutes of Health. The Lake Michigan Air Directors Consortium supported the aerosol sample collection for this project. The study was published July 29 in Applied and Environmental Microbiology.