Pseudomonas aeruginosa—an environmental bacteria that can cause devastating multidrug-resistant infections, particularly in people with underlying lung conditions—evolved rapidly and then spread globally over the last 200 years, probably driven by changes in human behavior, a new study has found.

People with conditions such as COPD (smoking-related lung damage), cystic fibrosis (CF), and non-CF bronchiectasis are particularly susceptible.

By mapping the data, the team was able to create phylogenetic trees—"family trees"—that show how the bacteria from the samples are related to each other. Remarkably, they found that almost seven in ten infections are caused by just 21 genetic clones, or "branches" of the family tree that have rapidly evolved (by acquiring new genes from neighboring bacteria) and then spread globally over the last 200 years.

This spread occurred most likely as a result of people beginning to live in densely-populated areas, where air pollution made our lungs more susceptible to infection and where there were more opportunities for infections to spread.