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Still no West Nile virus found in Utah humans

But misreading lab tests has led to false positives

West Nile virus has been detected in three more Utah counties. But there's still no evidence any human has acquired the virus in Utah.

However, misinterpretation of lab results has led a few health-care providers to tell patients, incorrectly, they have the virus. And that has created some confusion, according to Michelle Korth, an epidemiologist with the Utah Health Department.

The mosquito-borne virus has been confirmed in Grand, Duchesne and Wayne counties. It was first detected in Utah, Carbon, Uintah and Emery counties several weeks ago.

In Grand County, it was found in a dead crow. That's the only dead bird that's been found to have the virus, though 144 have been tested statewide. Health officials are still asking people to be on the lookout for dead crows, ravens, magpies, jays and similar large birds that are vulnerable to the virus.

The virus was confirmed in horses in Duchesne and Wayne County. It was found earlier in horses in Uintah and Emery counties.

West Nile also was detected earlier in batches of mosquitos tested in Uintah and Utah counties.

Several Utahns have been treated locally for the virus, but the state is confident those individuals acquired the illness during travel to other states, said Utah Health Department spokeswoman Jana Kettering.

A Wyoming resident apparently got the virus there but became ill while visiting Utah and was treated. Three Utahns apparently were bitten by virus-infected mosquitos in Colorado, Nebraska and North Dakota, respectively. All four are recovering.

But local labs have been testing people who have symptoms and have been to areas with West Nile virus, and that has led to some confusion.

The test looks for immunoglobulin G and M (IGG and IGM, respectively). In some cases, people have tested positive for IGG but negative for IGM, and their health-care provider has mistakenly told them they have West Nile. In fact, no one has tested positive for IGM, which is indicative of either St. Louis encephalitis or West Nile virus. Should someone test positive for that, the result would be confirmed by the state lab and the Centers for Disease Control and Prevention. It hasn't happened so far.

A "positive" IGG response could indicate a number of things, including prior exposure to a virus like yellow fever. It could mean the blood sample was simply reacting to something else, Korth said. It's not specific for West Nile.

"We don't consider being IGG-positive a positive for West Nile infection. But as they're reporting out these results, a lot of people mistakenly think it means someone has been infected with or exposed to West Nile," Korth said. "That's part of the entire confusion, and we're trying to educate the medical community."

Since mosquito season is reaching its peak, health officials are emphasizing the need to take precautions. That includes wearing long sleeves and pants when outside during the biting hours — from dusk to dawn. Folks should wear an insect repellent containing DEET and repair screens on windows and doors. It's also important to get rid of standing water to prevent mosquitos from breeding there.


E-mail: lois@desnews.com