My vet actually does not recommend heartworm prevention in this area. At his recommendation, and after doing my own research, I am very comfortable testing twice yearly but no meds. If a test were to come back positive I would be very comfortable treating with the slow-kill method, which is basically putting the dog on preventative with antibiotics on and off.
Interesting heartworm info, it has be above 60 degrees day and night for 30 days before heartworm can spread. In my area (northern NJ) that's about 2 or 3 months out of the year. In all my years of working as a tech I have never once seen a case of heartworm that has originated in my area. I have of course dealt with heartworm but every single time it's been a dog that has come from the south. Heartworm itself actually isn't that hard to treat or dangerous if caught early and a slow-kill method is used. Heartworm is dangerous when dealing with an untreated and advanced infestation that requires the use of immiticide (an arsenic based medication). Even then the biggest risk, provided it's not so far advanced that the dog is heading to heart failure (which usually takes about 6 years from initial infection) is pulmonary embolism caused by all the worms dying off at once. Recent studies have shown even that risk reduced though by the use of antibiotics prior to and during treatment.
I will say I wouldn't compare heartworm in humans to heartworm in dogs. Dogs are a heartworm's natural host and that causes dogs to have a much higher risk of contracting the worms in the first place and when they do the worms are able to breed within the dog and you can get a VERY high worm load in a dog that has gone untested/treated for a long time. IF a human contacts heartworm disease we usually max at a single worm that is unable to breed and dies off on it's own at the end of it's lifespan (a year or two if I remember correctly). There is really no comparison of the seriousness of heartworm disease in dogs vs. humans. Oh, and cats are basically like humans, they may get a worm or two but that's usually the extent of it, though it has been pushed recently to start cats on monthly prevention as well.