Concord Board of Health authorizes school perimeter spraying and urges dusk-to-dawn caution after EEE-positive mosquitoes

CONCORD — The Concord Board of Health on Saturday authorized the director of public health to sign emergency waivers permitting perimeter pesticide spraying at school properties and unanimously issued a strong recommendation that residents avoid nighttime outdoor activities from dusk to dawn after mosquito samples tested positive for eastern equine encephalitis (EEE).

The action followed notification from the North Middlesex Mosquito Control District that samples collected Sept. 5 and Sept. 10 tested positive for EEE, Melanie Deneneen, Concord’s director of public health, told the board. Chair Randy Krang read background from the Massachusetts arbovirus surveillance and response plan, including the plan’s assessment that EEE can lead to severe neurologic disease and carries a high mortality rate.

"Eastern equine encephalitis virus, a serious disease which occurs radically in Massachusetts, with 30 to 50 percent mortality, lifelong neurologic disability among many survivors," Krang read during the meeting, explaining the urgency of the emergency session.

Deneneen told the board the town had already sprayed perimeter vegetation at two municipal properties the previous Thursday and that several local schools — public and private — have requested emergency waivers to permit similar perimeter spraying on school grounds. "That emergency waiver must be signed by the agent of the board of health," she said. The board voted to authorize the health director to sign those waivers after a motion by Dottie Bernard, seconded by Jim Whalen.

The board emphasized the planned applications are to perimeter vegetation and not to playing surfaces. Deneneen said mosquito control identified a synthetic pyrethroid for the treatment (transcribed during the meeting as "delta methan"); the district entomologist present, Tony, described the product as having "low toxicity to humans" and noted it breaks down in sunlight. Town staff said treated locations would display posted signs for 72 hours after application.

Tony, the entomologist representing the mosquito control district, described the species found in Concord — Aedes vexans and Culex salinarius — and identified Culiseta melanura as the amplification vector in birds. He explained Aedes vexans tends to be active during daytime hours while Culex salinarius is a night biter, observations that factored into the board’s recommendation on nighttime activities.

Deneneen recommended that the board "encourage everyone to suspend nighttime activities until we get either our risk level changed down to moderate or we have a frost or cooler nights," while saying she did not believe daytime activities needed to be suspended but that people should take precautions such as repellent and long sleeves.

The board voted unanimously to "strongly recommend" curtailing outdoor activities from dusk to dawn based on Department of Public Health guidance; members and several public commenters discussed outreach measures including reverse 911, signage at high-risk trailheads, printed FAQs at playgrounds and schools, and notices on local outlets such as the Concord Bridge.

The board noted larvicide treatments for the season are complete and that natural cooling and frost are expected to reduce mosquito populations. Board members said they will continue to monitor mosquito surveillance results and state guidance and could revisit actions if additional positives are identified.

The board’s motions were procedural authorizations and public-health recommendations; no mandates or closures were ordered. The meeting closed after formal motions to adjourn.