The Baltimore City Health Department said Friday there was three confirmed cases of West Nile virus in the city, and officials are going door-to-door in the impacted neighborhoods with educational materials.
The unidentified people live in the 21224 and 21239 zip codes.
"Cases of West Nile virus are expected around this time of year," said Dr. Leana Wen, city health commissioner, in a statement. "We want to remind residents to be careful and to the take simple steps which can greatly reduce the risk of getting infected."
The first confirmed case in the state was in a Baltimore County adult in late August. Officials said the virus had also been detected in mosquito pools collected in Anne Arundel and Prince George's counties.
West Nile is transmitted by mosquitoes, so officials recommended that residents eliminate standing water, which serves as habitat for the larvae.
The virus doesn't sicken most people and most cases aren't reported. But symptoms can include fever, headache, body aches, rashes and swollen lymph glands within two to 14 days after a bite. Rarely, more severe symptoms occur.