Two Health or Not Two Health? That Is the Question

How much drug-resistant infections in livestock contribute to disease in humans is controversial. While zoonoses are a prominent cause of emerging infections, and the profligate use of antibiotics as growth promoters is expected to lead to the spread of resistance, this resistance could remain concentrated in animal pathogens and only rarely spill over into humans. A recent paper compares genomes of Escherichia coli isolates from human bloodstream infections in England, focused on the Cambridge area, with isolates collected from farms and the food chain in the east of the country, seeking evidence of transmission (C. Ludden, K. E. Raven, D. Jamrozy, T. Gouliouris, et al., mBio 10:e02693-18, 2019, https://doi.org/10.1128/mBio.02693-18). While the human and livestock populations were clearly distinct, with very limited evidence for transmission of E. coli or resistance elements to humans, the results also illustrate our limited ability to infer historical transmission events from even the best samples. The implications for the One Health framework, aiming to unify human and veterinary medicine, are discussed.