The first case of West Nile virus infection in Virginia this year has been reported in Fairfax County, coming on the heels of a confirmed case in Maryland.

Health department officials in Fairfax said the adult who contracted the disease lives in the northeastern part of the county. The person has been hospitalized and is recovering. Officials did not identify the person’s gender or age.

Last week, Maryland health officials reported the first confirmed case of a West Nile-infected adult in that state. Officials with the Maryland Department of Health said in a statement that the infected person lives in the Baltimore region.

Maryland’s Department of Agriculture said it also found the virus in mosquitoes collected in the Riverdale Park area of Prince George’s County.

Fairfax County health officials said they’ve seen a “large increase” in mosquitoes carrying the virus. The increase, officials said, is widespread across the county and has occurred earlier this summer than in previous years.

“In recent years, when one human case occurs in an area, other cases often follow in the same part of the county,” Fairfax officials said.

The number of confirmed infections can vary from year to year. Fairfax County health officials said they had five reports of people contracting West Nile last year but none in 2016.

In Maryland, there were five reported cases of West Nile last year, according to the Centers for Disease Control and Prevention. In Virginia, there were 13, and in the District, there were four.

West Nile virus, spread by the bite of an infected mosquito, can affect a person’s nervous system. Symptoms can include muscle aches, headache and fever.

Most people make a full recovery over weeks or months, officials said, but severe cases can lead to meningitis, paralysis and even death, according to experts. Less than 1 percent of those people contracting the virus will develop severe symptoms.

The most vulnerable to the virus are people age 50 and older and those who have weakened immune systems. Anyone who thinks they may be infected should see a doctor immediately, officials said.

Benjamin Schwartz, director of epidemiology and population health for Fairfax County, said that with the high levels of the virus in mosquitoes and recent rain leading to even more mosquitoes, it is important for residents to take precautions.

Officials provided several tips: Use a mosquito repellent that contains DEET; wear long sleeves and pants to protect skin; and avoid areas where mosquitoes are common during peak biting times, often dawn and dusk.

Officials also recommend dumping out standing water that can collect in old tires, planters, buckets, toys, flowerpots, trash cans and birdbaths.