Also worth mentioning that being displaced and robbed means that doing things like effectively quarantining become much harder, you are likely to be exposed to many other different diseases (native or otherwise) due to poor shelter, lack of medicine to prevent or treat infections, contact with different animal species and even human populations, etc., and really everything about the situation making the fact that there were any survivors basically accidental to the actual concern the colonizers had of making sure colonized land was "cleared" of native inhabitants.