(CNN) The Massachusetts Department of Public Health has reduced the number of deaths in the state from Eastern equine encephalitis from four to three, bringing the nationwide total to nine deaths.

"Based on an incorrect report filed by a hospital, DPH has been notified that the fourth death was improperly reported and the official death count remains at three people," the state reported in a statement Thursday.

Massachusetts health officials also announced the addition of a 12th case of the disease, a woman in her 70s from Hampden County.

There have also been three deaths in Michigan, two in Connecticut and one in Rhode Island.

Eastern equine encephalitis, known as EEE, is a rare virus transmitted by mosquitoes. There are typically only 5 to 10 human cases reported in the United States each year, according to the US Centers for Disease Control and Prevention. About 30% of all cases result in death. This year there has been an uptick in the number of reported cases, nearly 30 among several states.

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