The state announced four new cases of West Nile virus among Massachusetts residents Thursday, including three men in Middlesex County and a girl under age 19 in Bristol County.
Combined with three cases reported this summer, the total for the year is now seven, compared to five cases in 2019, the Department of Public Health said in a statement.
The Middlesex County infections included a man in his 40s, one in his 60s, and another in his 80s, the department said.
Based on information about where the four recently infected people were exposed to West Nile, the state elevated Cambridge, Newton, Somerville, and Watertown to high risk for the virus.
Concord, Dighton, Fall River, Lexington, Lincoln, Swansea, Sudbury, Waltham, Wayland, Weston, and Winchester were elevated to moderate risk for West Nile.
The virus has mostly been detected this year in an area around Boston that includes parts of Middlesex, Norfolk, and Essex counties, the state said.
West Nile is usually spread to humans through the bites of infected mosquitoes. Anyone can become infected, but people over age 50 are at higher risk of becoming seriously ill, the state said.
Most infected people do not become sick, but some will have fever and other flu-like symptoms.
The state encourages everyone to stay indoors between dusk and dawn, use insect repellent when outdoors, and wear long sleeves and pants to help prevent mosquito bites. Homeowners should remove or drain standing water and keep window screens in good repair, the state said.