There would need to be research done, nothing has been said if these people were all immigrants to Barcelona or the wages they were on, my guess is they are probably not truly random and replication will be difficult if we chose say bilingual in Wales, for example.
There is not reason to think that inmigrant population is over-represented in the hospitals. Would be more logical to expect the opposite, in fact, as some immigrants could be more reluctant to go to the hospitals.
