« The pathogens they carry include bacteria such as Clostridium difficile (C. diff), Salmonella, E. coli, and Leptospira. »
Well, humans definitely carry at least three of those as well...
« it is unclear how infectious the rats are to residents. »
And yeah, that's the crux of it. We don't actually know if it's a problem!
At a glance, rats are definitely ridden with fleas and disease, but there doesn't seem to be good data on transmissions. I'd still prefer not to have 10,000 tiny little catalysts for a new wave of the plague scuttling under my feet.