DISCOVERY BAY -- Mosquitoes from the Discovery Bay area tested positive for the West Nile virus this week, the first mosquito infection in Contra Costa County for the 2013 season, officials said Tuesday.

Three different groups of mosquitoes trapped near Bixler Road and Point of Timber Road tested positive for the virus, said Deborah Bass, public affairs manager for the Contra Costa Mosquito & Vector Control District. The detection in mosquitoes comes less than a week after the first confirmed West Nile case in Contra Costa County, which came in the form of a dead crow near Yellowstone Drive and Hillcrest Avenue in Antioch.

"Once the mosquitoes get the virus from birds, they can transmit it to people," Bass said. "It only takes one bite."

Since 2005, 42 people in Contra Costa County have been diagnosed with West Nile virus, and two people died from the disease in 2006. Recent studies have shown that the majority of cases are grossly underreported and often go undiagnosed.

A person who has contracted the virus might first notice fairly typical flu-like symptoms, such as fever, muscle aches and chills, Contra Costa district's lab director Steve Schutz said. If seeing a doctor for those symptoms, patients should tell their doctors if they've been bitten recently.

The breeds of mosquito most likely to carry the disease tend to be most active around dawn and dusk, Schutz said. Residents who will be outdoors during those hours can protect themselves by wearing mosquito repellent that includes the chemicals DEET, picaridin or oil of lemon eucalyptus.

The district will be fogging for adult mosquitoes in Discovery Bay on Wednesday evening, and residents are asked to drain any standing water to avoid giving mosquitoes a place to lay their eggs. They are also asked to report dead birds, which are often the first sign of West Nile virus in a given location.

According to Bass, reporting neglected swimming pools is also extremely important because they can produce more than 1 million mosquitoes that can affect people up to five miles away.

The district accepts anonymous reports of water sources where mosquitoes may be developing. Residents may contact the district to report mosquito problems at 925-771-6195.

Contact Erin Ivie at eivie@bayareanewsgroup.com. Follow her at Twitter.com/erin_ivie.