Public health officials said Monday there is a moderate risk that mosquitoes in Boston may be carrying the West Nile virus.
Anne Roach, a spokeswoman for the state Department of Public Health, said Boston had been upgraded from a low to moderate risk level.
“The change in risk level was based on an assessment of mosquito activity in the area,” Roach said in an e-mail.
Boston was one of roughly a dozen communities in the state with the moderate designation Monday evening, according to the department’s website. The rest of the state was deemed to be at low risk.
West Nile is commonly spread to humans who are bitten by infected mosquitoes and can cause fevers, inflammation of the brain, and meningitis, according to the US Centers for Disease Control and Prevention.
State health officials urge residents in areas at moderate risk to wear mosquito repellent, as well as long pants and long sleeves, weather permitting. They should also equip baby carriages and playpens with mosquito netting and dump standing water twice weekly.
Additional cities and towns at a moderate risk level on Monday night included Brookline, Northampton, Southampton, Easthampton, Abington, Brockton, Swansea, Fall River, Freetown, Westport, Dartmouth, and New Bedford.
Late last month, officials announced that the season’s first batch of mosquitoes infected with Eastern equine encephalitis, which is also passed to humans, had been detected in Amherst, an area not typically plagued by the virus.
Massachusetts has had no confirmed human cases of either virus this summer, Roach said. Last year, a 63-year-old Amesbury woman and a 79-year-old Westborough man died of EEE.
globe.com. Follow him on Twitter @TAGlobe.