Massachusetts health officials have raised West Nile virus risk levels to moderate across 10 Berkshire County communities and most of the state following the confirmation of the seventh human case of the season, a Worcester County man in his 60s.
Rising Human Cases Prompt Statewide Risk Level Adjustments
Mosquito season has tightened its grip across Massachusetts, prompting public health officials to elevate the West Nile virus risk level to moderate across most of the Commonwealth. The shift follows a series of confirmed human infections.
The state Department of Public Health confirmed its seventh human case involving a Worcester County man in his 60s, marking the first reported infection in that county. Prior to that diagnosis, officials recorded six other human cases, including a Suffolk County man in his 70s whose symptoms began on August 26 and who subsequently developed encephalitis, or inflammation of the brain.
According to state tracking, infected individuals this season include three men in Suffolk County—one in his 50s and two in their 70s—alongside three men in Middlesex County aged in their 60s, 80s, and 90s. As a result of this widespread transmission, almost the entire state now sits at a moderate risk level.
Only Dukes and Nantucket counties, alongside the Barnstable County towns of Provincetown and Truro, remain categorized at low risk. In Berkshire County, health officials moved Sandisfield, Otis, Monterey, Tyringham, Lee, Stockbridge, West Stockbridge, Richmond, Alford, and Egremont into the moderate-risk category, leaving only six towns in the county below that threshold.
Surveillance Data for the Season
The expansion of the virus aligns with national observations. West Nile virus remains the most common mosquito-borne illness in the United States, according to the Centers for Disease Control and Prevention.
Within Massachusetts, vector surveillance has detected the virus in 307 mosquito samples spanning every county except Nantucket since the first positive pools were announced in mid-June. By contrast, Eastern Equine Encephalitis has been detected in 14 mosquito samples statewide, with no reported human or animal cases.
“Mosquitoes remain active, and West Nile virus continues to spread.”
Dr. Robbie Goldstein, state public health commissioner
While Berkshire County has not recorded a human case, local trapping identified three additional positive mosquito samples: one collected in Lanesborough on August 25 and two retrieved from Otis and Richmond on August 27. Health authorities emphasize that while many human infections present mild or unnoticed symptoms, roughly 1 in 150 cases progress to severe, potentially life-threatening illness, with individuals over 50 facing the highest risk.
Public Health Guidance Ahead of Labor Day and Autumn Frosts
With outdoor activities peaking around holiday weekends, state health leaders have renewed warnings for residents to maintain precautions. Because no human vaccine or specific medical treatment exists for West Nile virus, prevention relies entirely on personal protection and vector reduction.
Public health officials advise residents to eliminate standing water twice weekly from containers such as kiddie pools, flowerpots, gutters, and discarded toys to disrupt breeding cycles. When outdoors, individuals should wear long-sleeved clothing, utilize insect repellent, and ensure window and door screens remain properly repaired. Families with infants are instructed to cover carriages and playpens with mosquito netting.
“Because some risk will continue until the first hard frost, I want to encourage everyone to keep using mosquito repellent and take other protective measures.”
Dr. Robbie Goldstein, state public health commissioner
State guidance stresses that active transmission will persist until the season experiences its first hard frost, making continued vigilance necessary throughout September.
