West Nile virus activity is slowing and active surveillance will stop next week in most of the state. But health officials say people need to keep using DEET repellents and taking precautions into early October.

The last sentinel chickens will be bled and tested Monday, dead birds swabbed and mosquitoes trapped in the next few days. But the virus will be active throughout the state for at least a few more weeks.

Surveillance is done to show when the virus is active in an area and to what degree, says Lisa Wyman, an epidemiologist in the Utah Department of Health.

"We know it's here. And we think it's winding down, but that doesn't mean it's going to be gone, at least through September. People need to take the same precautions. We expect to see human cases reported into October. There will still be people getting sick in the next three weeks, but at lower levels than when it was hitting its peak in summer."

Today's update of confirmed cases by the Utah Department of Health is expected to show nearly 100 for the season. It's an undercount, and so is the list of counties infected. "Where it says no activity, we have it, we just don't have a lot of surveillance. It's probably in every county in Utah to some degree," Wyman says. Three West Nile deaths had been confirmed in Utah by Sept. 9.

Stopping surveillance is largely "a function of personnel," she says. Mosquito abatement districts boost their staff levels over the summer and reduce them in the fall.

Although Utah was much harder hit this year than in previous years, its infection rate pales compared to Idaho, which had about 700 confirmed cases as of last Friday in southern and central parts of the state. West Nile killed nine elderly Idahoans and sent many to the hospital.

The Centers for Disease Control and Prevention marks the Gem State as the definite virus hot spot this year, a distinction that in the past has gone to other Utah neighbors, including Arizona and Colorado.

An Idaho Department of Health and Welfare spokesman, Tom Shanahan, believes agricultural irrigation may be partly responsible for his state's toll this year.The affected part of the state is dotted with irrigation canals and sprinklers, then and a heat wave hit in July making a happy breeding ground for the mosquitoes. Many of the infections were in such areas, including the southwestern portion of the state near Boise and near Blackfoot on the southeastern side. Counties near those were much less affected, and the panhandle didn't have any.

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.