Five Santa Clara County residents have become infected with West Nile virus, including one person who is currently hospitalized.

In releasing word of the infections, health officials say besides the person being cared for in a hospital, two others were hospitalized and later released. Two other people who were confirmed to be infected with West Nile but showed no symptoms.

The five cases are the first confirmed West Nile infections of humans in Santa Clara County this year. Officials did not release the names, ages or genders of the people infected with the virus but said all five live in areas of the county where there is a high level of West Nile virus activity.

Dr. Sara Cody, Health Officer for the county, issued a statement Friday urging area residents to take precautions:

“It is important to remember most people who get a mosquito bite will not become infected, will not develop symptoms and will not need to seek care. But in some cases, West Nile can cause serious illness. To reduce the risk of West Nile, residents should take precautions to avoid being bitten by mosquitoes.”

Besides the five humans getting the virus, Santa Clara County officials say they have found 648 dead birds infected with West Nile virus, an amount described as “unusually large.” It’s also half of all the reported dead birds found infected with the virus in the state.

With so many dead birds being found with the disease in the county, health officials warn the risk of more humans becoming infected with the virus “is likely to be higher than in previous years, especially over the next few months.”

Health officials are providing information to doctors on how to recognize and diagnose the disease. They’re also asking physicians to report suspected cases to the California Department of Public Health.

Last week, the department reported the first two deaths of the summer from the disease — one person in Sacramento County and person in Shasta County died from West Nile virus.

In move to try to eradicate infected mosquitoes — the prime transmitter of the disease — vector control officials have been “fogging” areas of Santa Clara County, as well as parts of San Mateo County, since late May .

More fogging — or using trucks with special equipment to release a chemical officials say is considered a “reduced risk” chemical by the Environmental Protection Agency — is planned for Tuesday night in parts of Sunnyvale and Mountain View.

John Marshall is an SFBay editor and producer and writer for San Francisco’s KGO Radio. Follow him on Twitter @breakingnewsman.