As mouse-killers their efficiency varies enormously. Few of them really come up to scratch. They cannot often get into areas where mice can live in a building.
In addition most house cats have lost the hunting ability of a good farm “mouser” and may even bring live rodents into properties.
Cats are unacceptable in food preparation areas and, indeed, wild cats breeding under hotels and hospitals can be reservoirs of flea infestation as well as causing problems with noise and smell.
Feral cat (or stray cat, alley cat) is a cat which has been separated from domestication through abandonment, loss, or running away, and becomes wild. The term may also refer to descendants of such cats, but not to wild cats, whose ancestors were never domesticated.
Feral cats may live alone but are usually found in large groups called feral colonies.