A complicated subject. Suggest that you do a Google search for - fire blight + host plants. Read through those threads carefully for an understanding of the problem. The easiest solution is to remove those host plants growing in your yard. Hopefully they are not also growing in your neighbors landscapes. It is quite possible that the pear tree is the source of your infection...or, apple, flowering crab, firethorn, hawthorn, cotoneaster, quince, Mountain ash and as noted, pear.

Fire blight is a tough one to control. Much better to bite the bullet and remove the host plant(s) causing the infection.