I know that rats can be very cautious of anything new in their environment and it can take awhile for them to try something new. Do you know what they are eating in your neighbourhood? You should wear gloves when setting and baiting traps as the smell of humans can make them avoid the traps. Some species of rat like carbohydrates and some prefer protein, so perhaps do a combo of the two and see if that ups your chances of catching some. I'd use the same bait for a week before switching it. Hopefully you can start to get on top of this awful problem, and I'm sorry you aren't getting any help from your health department. That makes it even harder.
