More development.  Less habitat.  Rats move into human populated areas.  All humans do not have homes or the ability to deal with vermin.  Rats carry disease, usually bacterial, that can kill humans.... quickly.  Plagues still occur world wide.  So, get filth and waste disposed of from areas were people gather.  Near rivers, under freeways and in areas where people and rats may share common space.   Providing showers, rest rooms, medical supervision an medication (antibiotics is a good start) to those that cannot afford it. This is not about agriculture or pesticides or other nonsense.  It is about killing rats.  The more rats you exterminate the safer our communities will be.  Should we be concerned....darn right.  Contact the State of Hawaii Vector Control and see how many inspectors are actually working.  I hire a private pest control company to treat my residence and yard. Wife saw a rat in our garage.  Called pest control company. Caught and disposed of the rat in two days.  Happy