I should have been more specific since NY is so large- I am in Western NY and hardly ever see mosquitoes except during warm summer nights or near ponds. Guess I am glad for that, both for me and my dog. Do you see many HW positive dogs that live inside and are typically 'well cared for' by most standards? It always seems that dogs in rescue that are positive around here are dogs that lived outside and were in general, neglected. I have read some about the failure of some brands (many Heartgard) where dogs that were dosed yearly still came up positive. Do you see many of those cases?
Yes, I see cases that are well loved pets that rarely go outside. Those are the hardest to see, because the owners are so upset at themselves for forgetting a dose or two of prevention.
I haven't see a true prevention failure (client swears they never missed a dose) in the northeast, but I suspect that has to do with numbers (fewer months of exposure up here). I did see it when I lived in a heartworm endemic area. The companies paid for treatment as long as the owners could prove they purchased a full 12 months worth of prevention from a vet (they don't honor that guarantee if you purchase via other sources). I went to a conference where the comment was made that most of the failures were with topical products, but the suspicion was that it was a client problem (failure to apply the entire vial) in most cases.
BTW, the worst problem I have seen to date from spinosad is self limiting vomiting. I do use a private label version of Trifexis on my dogs. When it wasn't available I was using a product with the same active ingredients as HG+.