An individual’s microbiome is sometimes indicative of his or her health, but what about the entirety of a population. Can a city’s microbiome be indicative of the health of that city’s population? In an article published in MBio, researchers collected sewage samples from 71 U.S. cities in the hopes that it would accurately reflect the microbiomes of that city’s citizens.

Researchers collected and sampled sewage from 71 cities and 78 waste water treatment plants across the United States, and compared it to publicly available data from the human microbiome project. They discovered that the sewage samples were representative of the human stool samples, and that they captured 97% of the bacteria found in the typical stool. In addition, they noted that sewage samples had a greater bacterial diversity than stool samples. The researchers also identified 27 “core” gut bacteria among all the sewage samples that they suspect are ubiquitous across the American population.

Interestingly, the researchers were also able to use their data to predict, with 81-88% accuracy, whether the sample came from a lean or obese population. The relationship was driven mainly by an increased abundance of Bacteroides and a decreased abundance of Faecalibacterium. While Faecalibacterium are more present in high-diversity anti-inflammatory gut communities, Bacteroides are found more commonly in gut communities of human consume a diet high in animal fat.

This study demonstrates that sampling sewage may be a practical way to attain large samples of human fecal microbiome, in order to compare populations without bias. It must be unpleasant to work with fecal samples to begin with, so attaining samples from sewage may be an easier alternative, especially in studying populations, as opposed to individuals.