No, that phenomenon is a result of genetic stagnation. Population density is only bad if hygene is poor and social services (*ahem* health care *ahem*) are poor. Otherwise, there's nothing wrong with it.
The H041 outbreak doesn't exist. H041 was one strain found in Japan that was never found again. MRSA is a result of overuse of antibiotics, especially in livestock feed, where much of it runs off into groundwater in minute quantities. And antibiotic resistance transfers between bacteria, so one bacteria that develops resistance can basically "infect" its neighbors to also be resistance.
None of this is due to population density. There are numerous places with much higher population density, without so many widespread health issues. The anti-social behavior of American culture doesn't help either.