HOLLISTON (CBS) – The Massachusetts Department of Public Health raised the risk level of Eastern Equine Encephalitis to “critical” in Holliston, Medfield, Brookfield and Granby on Thursday. Horses in each community tested positive for the mosquito-borne EEE.

There are now 28 communities at a critical risk level, with 37 more at a high risk. So far there have been four confirmed human cases of EEE, including the death of a Fairhaven mother.

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“As we head into the Labor Day weekend and the month of September people should not forget to bring and use an EPA-approved mosquito repellent for any outdoor activities,” Public Health Commissioner Monica Bharel said in a statement. “The peak time for transmission of mosquito-borne illness extends through September here in Massachusetts.”

Belchertown, Brimfield, Chicopee, East Brookfield, Ludlow, Medway, Millis, North Brookfield, Sherborn, South Hadley, Sturbridge, Walpole and West Brookfield all saw their risk levels raised to high on Thursday. EEE has now been detected in 366 mosquito samples in the state this year, and the department said many of those species can pass the virus to people.

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The latest EEE risk map (Image credit: Massachusetts Department of Public Health)

EEE symptoms can range from a stiff neck, headache, and lack of energy to dangerous complications like inflammation and swelling of the brain. The risk of EEE will remain until the first killing frost.

Both Holliston and Medfield officials are discouraging outdoor activity after dusk. Medfield school sports practices will end by 7 p.m. and night games are being rescheduled.

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The state is urging residents to use insect repellent when outside, wear protective clothing and rescheduling activities in the early morning and evening hours.