A map showing the risk of EEE infection by town across Massachusetts as of Friday, Sept. 27, 2024.
Four people in Massachusetts have been diagnosed with the rare mosquito-borne virus eastern equine encephalitis, or EEE, so far this year, according to the Massachusetts Department of Public Health. It's led some communities to advise residents to limit outdoor activities when mosquitoes are most active, at dawn and dusk.
Of those who develop severe symptoms of EEE, 30% die, according to the U.S. Centers for Disease Control and Prevention, and survivors can have long-term neurological issues.
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Massachusetts has reported the most EEE cases of any state this year — New Hampshire, with two, is the only other state with more than one case, according to CDC data, last updated Tuesday. The last EEE outbreak in Massachusetts, from 2019-2020, led to seven deaths among 17 cases in people. But it's not yet public information whether any of Massachusetts' four reported human EEE infections this year have resulted in the person dying, under current Department of Public Health policy.
While New Hampshire shared last month that its first EEE case in 10 years resulted in a man's death, Massachusetts has not reported whether or not any of the four people who've been infected have died. The announcements on each case have only included the sex and general age of the person who was infected, as well as what county they were exposed in.
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The Department of Public Health has told NBC10 Boston that the number of fatalities tied to EEE will be released to the public, as well as to the CDC, after the season ends, which is when the first hard frost freezes the ground.
State epidemiologist Dr. Catherine Brown spoke about the policy in an interview with New York Magazine published on Friday, acknowledging both the need to keep the public informed and the need to keep patients' information private.
"So right now, we’re providing information about the sex of the person, their age range, and then the location where we think they were exposed to the virus," Brown told the magazine. "When you start to add additional information, like whether the patient was hospitalized or their current status, including whether they have passed away or not, it makes it easier to identify people. Also, [EEE] is a very significant infection. People don’t always just die or recover in a very short period of time. And so it often takes time to really understand what the outcome is of all of our patients."
Massachusetts has previously announced EEE deaths in news releases as they happened. The Department of Public Health has told NBC10 Boston that the current policy of sharing aggregate statistics at the end of the season dates to 2019, and has cited patient privacy for not sharing more information on individual cases of mosquito-borne viruses.
Asked about the policy, Boston University professor and public health and infectious disease expert Dr. David Hamer said it seemed like a reasonable approach to reporting mortality. It's a complex issue, he said, given that it can take time to link a person's death to EEE.
"After a few challenges determining association between EEE and patient deaths, the state of Massachusetts is now cautious and has decided to release a final summary at the end of the season when they have full information," he said in an email.
State health officials have been consistent in urging caution for anyone in an area at high risk for EEE transmission, including on Thursday, when the state announced a third Massachusetts horse was diagnosed with the virus this year.
"Cooler temperatures will start to reduce mosquito activity, but people shouldn't let their guard down yet," Brown said in a statement. "We continue to strongly advise that everyone in areas at high and critical risk for EEE reschedule evening outdoor activities to avoid peak mosquito biting hours."
Public Health Commissioner Dr. Robbie Goldstein echoed that sentiment, saying, "This latest animal case of EEE confirms that even this late in the season, the risk for spread of EEE virus from infected mosquitoes is still present," and urging that people going outside continue to protect against getting bitten by mosquitoes.
