Massachusetts health officials confirmed three more human West Nile virus cases on Sept. 25, raising the state's 2026 total to 11. The new patients are a man in his 60s exposed in Suffolk County, a man of unknown age likely exposed in Suffolk County, and a man in his 90s exposed in Middlesex County, according to the Massachusetts Department of Public Health (DPH).
Risk remains high in Boston, Brookline, Cambridge, Chelsea, Everett, Malden, Newton, Revere, Somerville, Watertown, and Winthrop. Most of the rest of the state is at moderate risk. Officials said the risk will continue until the first hard frost.
The count rose quickly. The state had reported eight cases a week earlier, on Sept. 18. For Greater Boston households, cooler evenings are not yet a reason to put the repellent away, especially for older relatives who spend time outdoors around dusk.
Suffolk and Middlesex Exposures Drive the Season
Ten of this year's 11 cases involved confirmed or likely exposure in Middlesex or Suffolk counties; the other was a man in his 60s exposed in Worcester County. The eighth case, announced Sept. 18, was a woman in her 30s exposed in Middlesex County, the first woman reported with the virus in the state this year, according to the Boston Globe.
Mosquito testing shows how widely the virus is circulating. Since the state's first positive mosquitoes of the year were detected on June 16, 338 mosquito samples have tested positive for West Nile. Positive samples have come from 13 counties: Barnstable, Berkshire, Bristol, Dukes, Essex, Franklin, Hampden, Hampshire, Middlesex, Norfolk, Plymouth, Suffolk, and Worcester.
No animal West Nile cases have been reported this year. Eastern equine encephalitis (EEE), a rarer and often more severe mosquito-borne virus, has been found in 26 mosquito samples, with no human or animal cases so far, according to Western Mass News.
The age pattern is familiar. Nine of the 11 patients are men in their 50s or older, including two in their 90s. That matches the virus's long-standing risk profile, although this season's cases also include a woman in her 30s.
Older Adults Face the Most Serious Illness
Public Health Commissioner Robbie Goldstein, MD, PhD, singled out vulnerable residents in a state update on Aug. 31. "People who are older or have compromised immune systems are especially at risk from this disease," he said. He urged residents to keep using repellent, cover up, consider staying indoors from dusk to dawn, and empty anything collecting water outside. "The mosquitoes will be with us until the first hard frost," he added.
State Epidemiologist Dr. Catherine M. Brown said in the same update that more than 275 Massachusetts residents are known to have been infected since the state's first human cases in 2001, most with the severe form that affects the central nervous system. That figure counts only known infections.
Most people infected with West Nile have no symptoms, according to the CDC. Some develop fever with headache, body aches, joint pain, vomiting, diarrhea, or rash, usually two to six days after a bite. Fatigue and weakness can last for weeks or months.
A smaller group develops severe illness affecting the brain or spinal cord. Warning signs include high fever, headache, neck stiffness, disorientation, muscle weakness, and seizures. These symptoms need prompt medical care, and patients should tell their provider about any recent mosquito exposure.
There is no licensed vaccine or medicine to prevent or treat West Nile virus disease in people. Care for severe cases is supportive, which is why officials focus on preventing bites.
Repellent, Dusk Precautions, and Yard Checks Through First Frost
State guidance is practical and inexpensive. Residents should use a repellent with an EPA-registered ingredient, such as DEET, picaridin, or oil of lemon eucalyptus, and follow label directions. The state also lists permethrin, which is used to treat clothing and gear rather than skin. DEET should not be used on infants under 2 months and should be used at a concentration of 30% or less on older children. Oil of lemon eucalyptus should not be used on children under 3.
Peak biting time runs from dusk to dawn. In high-risk communities, officials recommend rescheduling evening and early-morning outdoor activities when possible, which may affect youth sports practices, evening dog walks, and outdoor dining. Long sleeves, long pants, and socks add another layer of protection.
Standing water deserves attention, especially after the heavy rain the late-September nor'easter brought to much of the state. Residents can empty flowerpots and wading pools, check gutters and drains, change birdbath water often, and repair window and door screens.
Adults over 50, older relatives living alone, people with weakened immune systems, and outdoor workers in the 11 high-risk communities have the most to gain from these steps. Family members can make sure an older parent has repellent at home and knows which symptoms call for a doctor.
Residents with questions can call the DPH Division of Epidemiology at 617-983-6800.
Case Updates Expected Each Friday
DPH has said it will update the public on West Nile cases through weekly press releases each Friday, while surveillance information, including case updates, is posted daily on its Massachusetts Arbovirus Update page. Last year, the department lowered high-risk municipalities to moderate at the end of October, noting that some risk would remain until a hard frost.
The newest numbers do not mean every resident faces the same danger. They show that infected mosquitoes are still active across Greater Boston in late September and that severe illness remains most likely in older adults. Consistent repellent use, extra care around dusk, and quick medical attention for neurological symptoms remain the best protections until the first hard frost.
Key Questions Answered
How many West Nile cases has Massachusetts reported in 2026? Eleven human cases as of Sept. 25, after three new cases were announced that day.
Which communities are at high risk? Boston, Brookline, Cambridge, Chelsea, Everett, Malden, Newton, Revere, Somerville, Watertown, and Winthrop. Most of the rest of the state is at moderate risk.
Who is most at risk of severe illness? Older adults and people with weakened immune systems or certain chronic conditions face the highest risk of illness affecting the brain or spinal cord.
What symptoms need urgent care? After possible mosquito exposure, seek prompt care for high fever, headache, stiff neck, disorientation, muscle weakness, or seizures.
When does the risk end? State officials say West Nile risk continues until the first hard frost.
Has EEE been found in people this year? No. Officials have detected eastern equine encephalitis in 26 mosquito samples, but no human or animal cases have been reported.
Published by Medicaldaily.com
