The state has raised the West Nile virus risk level to high in Chelsea, Revere, Winthrop and Everett, and the mosquito season that produces most human cases in Massachusetts still has several weeks to run. The upgrade for Chelsea, Revere and Winthrop came on September 4, after the Department of Public Health confirmed the state’s sixth human case of the year, a man in his 70s who was most likely exposed in Suffolk County. Everett was raised to high on August 26 after a human case in Middlesex County.
None of this is abstract for the four communities. West Nile was confirmed in a mosquito collected in Chelsea on August 20. Revere and Winthrop both posted notices of positive samples the same week. By September 4 the state had found the virus in 273 mosquito samples across 13 counties, including Suffolk and Middlesex, which cover all four cities and towns.
What high risk means
DPH uses a four-step scale, from remote to high, based on how much virus is turning up in mosquito traps, how late in the season it is, and whether people or animals have been infected nearby. High risk does not mean the state is spraying your neighborhood or canceling outdoor events. It means the odds that a bite from a local mosquito carries the virus are as high as they get in Massachusetts, and that the people most at risk of serious illness should act accordingly.
Most people who are infected never know it. About one in five develop a fever, headache, body aches, and sometimes a rash. A small fraction, well under one percent, develop the serious neurological form of the disease, which can mean encephalitis or meningitis and can be fatal. The risk of severe illness rises sharply after age 50, which is why the state’s guidance singles out older adults. Massachusetts recorded 131 human cases between 2014 and 2023, with 11 in 2021, 8 in 2022 and 6 in 2023. This year’s count reached six by the first week of September.
What each community is doing
Chelsea’s Board of Health has said the city treats catch basins with larvicide, which kills mosquito larvae in the standing water beneath storm drains before they can fly. That is the main tool in a dense city with little open land, and it is invisible to residents.
Revere is offering something residents can actually see. Through the Northeast Massachusetts Mosquito Control and Wetlands Management District, Revere residents can request free spraying of their property by calling the district at (978) 352-2800, or (781) 485-8486 for information. The Revere Journal reported the offer would run about one more week from September 9, so anyone who wants it should call now. Revere’s health department also said it maintains weekly spraying protocols and has been doing outreach to older residents.
Winthrop posted a public health notice on August 20 after the virus turned up in local samples and was included in the September 4 upgrade. Everett has been at high risk since late August; the city’s notice pointed residents to the state’s prevention guidance and did not describe additional spraying.
What to do about it
The advice from every one of these health departments is the same, because it works.
- Repellent. Use a product with DEET, picaridin, IR3535, or oil of lemon eucalyptus, and follow the label. Permethrin can be applied to clothing but not skin.
- Timing. The mosquitoes that carry West Nile are most active from dusk to dawn. If you are out then, cover up: long sleeves, long pants, socks.
- Standing water. The species that spreads West Nile breeds in small, dirty pools. Empty flowerpot saucers, wading pools, buckets, tarps and wheelbarrows. Change birdbath water twice a week. Clear gutters.
- Screens. Repair or replace window and door screens so mosquitoes stay outside.
Older adults and anyone with a weakened immune system should take these steps seriously through the first hard frost, which in this part of the state usually does not arrive until well into October. Anyone who develops a high fever, severe headache, stiff neck or confusion in the weeks after mosquito exposure should see a doctor and mention it.
The state posts current risk levels by municipality and positive sample results at mass.gov/dph/mosquito.
Sources: Massachusetts Department of Public Health announcement, September 4, 2026, as reported by Boston 25 News and This Week in Worcester; Chelsea Record, August 20, 2026; Everett Independent, August 26, 2026; Revere Journal, September 9, 2026; City of Revere Department of Public Health; Town of Winthrop public health notice, August 20, 2026; DPH historical case counts as cited by the City of Revere. Photo: Culex pipiens, by Volkmar Becher via Wikimedia Commons, CC0.