The year following such an active West Nile season, other states have seen dramatic drop-offs. Shanahan says some health experts believe people may be developing a kind of immunity to the virus, although no one knows how long that protection will last.

Climate so far has worked in Utah's favor as far as protecting from a massive number of cases, Wyman says. In both Arizona and Colorado, the big impact was in non-desert areas like Phoenix. She also credits "outstanding" mosquito abatement efforts in Utah.

State health officials hope that counties down south with warmer temperatures will keep up their own surveillance efforts until it becomes cooler, Wyman says.

Meanwhile, mosquito abatement is a year-round process, she says. The districts are still killing adult mosquitoes. Nature won't step in to help significantly until there are good, hard frosts. And even then, some of the bugs will overwinter.

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