EDIT, with a relevant source for context:
Since 1940, an estimated 50% of zoonotic disease emergence has been associated with agriculture (1–3). This estimate, however, is necessarily conservative because only direct agricultural drivers are considered in the epidemiological literature, i.e., within the farm gat
[…]
The intensification of animal agriculture through confinement and industrialization has directly led to the emergence of viruses including Nipah and H5N1 influenza (“swine flu”) (18) and antibiotic-resistant infectious bacteria including methicillin-resistant Staphylococcus aureus and Escherichia coli (19, 20).
They were the most likely culprit in the H1N1 swine flu epidemic that almost killed a guy I know (he was a pretty healthy 20-something and had to be put on a ventilator and induced coma). The cause of that epidemic was related to literal lakes of untreated pig feces generated by factory farms and likely spread to humans via flies.