I think Susan's comments are spot on.
Like Susan I have not heard of chloroquine-resistant strains in Belize and the CDC recommends chloroquine for Belize, where it says (the CDC tends to be very conservative) there is a risk in all areas except Belize City.
Personally, I've been banging around Belize for about a dozen years and have been to just about every nook and cranny. I usually DO take chloroquine when I am in the far south and usually do not when I've just on the cayes or in Cayo, but chloroquine is safe, relatively cheap insurance and certainly one should pay attention to what the CDC and one's doctor says. Few if any expats in Belize take any malaria prophylaxsis, but I do know some who have had malaria. I personally don't know of any tourist who has gotten malaria in Belize but probably that has happened at least a few times.
In a separate message I'm posting the current information on malaria in C.A. and Mexico from the CDC (www.cdc.gov