The number of mosquitoes testing positive for West Nile virus reached new heights in the Coachella Valley this week, vector control officials said Wednesday.

The Coachella Valley Vector Control District collected 29 samples of mosquitoes with the virus in the last week, bringing the total number of positive samples collected this year to 108, according to the district’s Tammy Gordon.

At this time last year, no West Nile-positive mosquitoes had been detected, Gordon said.

The most recent samples were collected from communities across the valley, including Coachella, Indio, Mecca, Thermal and La Quinta.

Gordon said the sample collected from La Quinta marked the first time West Nile virus has been detected in that city so far this year.

There have been no reports of humans infected with the virus in California this year, but three people in Arizona have tested positive.

Vector Control District staff plan to post disease notification signs near the trap locations where West Nile Virus was detected and will increase surveillance and inspections for standing water sources, where mosquitoes can lay eggs, Gordon said.

West Nile virus is transmitted to humans through the bite of an infected mosquito. Most infected people will have no symptoms, but about one-fifth of those infected will develop fever, headaches and body aches, according to the Centers for Disease Control. About one in 150 infected people will develop a serious and sometimes fatal illness.

Risk of infection can be reduced by using insect repellent and wearing long-sleeved shirts and long pants to prevent bites from mosquitoes, according to the CDC.

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