In 2013, a team of Danish researchers gathered the poop from 18 airplanes that departed from nine cities and all landed at the Copenhagen airport. They sequenced the genomes of the microbes in the poop, and found some pretty interesting trends. Microbes that came from Southeast Asia had a much higher incidence of antibiotic resistance compared to those from North America—likely because antibiotics are still over-prescribed in Asia, the study authors hypothesize. Food-transmitted microbes Salmonella enterica and norovirus, both of which can cause vomiting and diarrhea, were also more frequent in the stool from Southeast Asia. That's supported by epidemiology data from the World Health Organization, the authors note, that shows people in Southeast Asia are much more likely to get food poisoning. The killer antibiotic-resistant bacterium Clostridium difficile was more common in the samples from North America, where it infects 500,000 people per year, mostly in hospitals.