IN THE SUMMER of 2013, researchers at the Technical University of Denmark headed to the Copenhagen airport for a special delivery: poop. The crew who clean out airplane toilets had siphoned it from flights arriving from around the world just for them.
Back in the lab, the researchers turned the samples into DNA soup and fed them through a sequencing machine. Out the other end came antimicrobial resistance genes and potential pathogens—all traceable to the individual plane’s country of origin.[snip]
From the airplane waste, the Danish researchers could identify regional patterns. Genes for antimicrobial resistance, for example, were more abundant in samples from South Asia than North America. They found differences in specific bacteria, too: Salmonella enterica, which can cause diarrhea, was more common in South Asian samples while Clostridium difficile, the bacteria behind a difficult-to-treat hospital-acquired infection that often follows a course of antibiotics, was most common in North American samples.