Less than a week after taking the rare step of raising the statewide West Nile Virus risk to moderate, state public health officials have now announced four human cases of the virus. The latest human case is a Middlesex County woman in her 50s who officials say was never hospitalized for her illness. Her case was announced Monday after three other human cases were made public on Friday - a woman in her 70s from Worcester County, a woman in her 60s from Middlesex County, and a woman in her 50s from Suffolk County.

The risk level for West Nile Virus has been raised to high in Arlington, Boston, Belmont, Brookline, Cambridge, Chelsea, Everett, Medford, Newton, Somerville and Watertown. State officials are recommending that local officials in those communities "intensify messaging" to raise awareness and work with mosquito control officials on appropriate prevention measures.

"It is extremely important for people to take steps to avoid mosquito bites, including using repellents, wearing clothing to reduce exposed skin, dumping standing water, and moving indoors when you notice mosquitoes biting you," Catherine Brown, the state epidemiologist, said in a statement late Monday. Officials identified six human West Nile cases in 2017.

Public Health Commissioner Monica Bharel last week said that the recent hot and humid weather, combined with frequent rainfall, have provided "perfect conditions for mosquito species carrying West Nile Virus to breed."