Worcester has raised its West Nile virus risk to moderate after a positive mosquito was found in the city, prompting a spraying operation as weather allows.

There have been no reported human West Nile virus cases in Worcester or Fitchburg at this time.

Older adults over 50 are at higher risk for severe West Nile symptoms, with nine Massachusetts human cases reported in 2025.

Residents should close street-facing windows, disable outside air settings on air conditioners, keep pets indoors from sunset to midnight, avoid children playing near spray trucks, stay indoors during spraying and for 15–20 minutes after, and wash home-grown vegetables after spraying before consuming.

During spraying, keep windows closed, pets inside, and remain indoors for 15–20 minutes after application; the spray is oil-based and dissipates quickly.

Also, wash homegrown produce after spraying and note that pets are not expected to be adversely affected by the pesticide used.

A map shows the spray area, which includes Circuit Avenue East, Minthorne Street, Lovell Street, May Street, Park Avenue, Maywood Street, and Spaulding Street.

People with chemical sensitivities should consult a physician; general precautions include using DEET repellents, wearing long sleeves and pants, and removing standing water to reduce mosquito breeding.

Accidental exposure is not expected to cause health concerns for most people, and no precautions are needed the day after application.

Preventive measures include eliminating standing water, using repellents, wearing covering clothing, and keeping screens intact; updates will come via ALERT Worcester and mass.gov resources.

A new spraying round is planned for the night of Thursday, August 6, weather permitting, targeting nearly 30 city streets in the southeast; if weather delays, spraying would move to Friday.

Residents may opt out of wide-area pesticide applications through the Massachusetts Department of Agricultural Resources.