A Suffolk County woman is the third person in Massachusetts this year diagnosed with the mosquito-borne West Nile virus, the state Department of Public Health announced Friday.
The woman, in her 60s, was hospitalized and released. A Norfolk County man in his 30s and a Plymouth County man in his 70s were diagnosed last month with the virus, which can cause fever and flu-like symptoms.
Last year, 33 people were confirmed to have West Nile. The virus is the less harmful of two illnesses carried by mosquitoes that place public health officials on high alert in late summer and early fall.
A Norfolk County woman died last month of Eastern equine encephalitis, the first fatal case of the year. Infections with that virus, which killed three people in Massachusetts in 2012, are uniformly considered serious.
But most people infected with West Nile have no symptoms at all. The virus poses the greatest risk to people over age 50.
A spokesman for the Boston Public Health Commission said the Suffolk County woman is not from Boston; state authorities would not disclose where she lives. West Nile virus has been found in mosquito samples collected throughout the city, including in East Boston, North Dorchester, Hyde Park, Roslindale, West Roxbury, Jamaica Plain, and Fenway.
The mosquito-borne illnesses remain a threat until the first hard overnight frost, said Dr. Catherine Brown, state public health veterinarian.
“People need to continue to use insect repellant, cover up exposed skin, and avoid being outdoors at dusk and after nightfall when mosquitoes are at their most active,” Brown said.
The state tracks risk levels for both viruses in every city and town in maps posted on its website. Suffolk County’s risk level for West Nile remains moderate. It would be increased if infections were confirmed in multiple people.
The Eastern equine risk level for the county is the lowest possible, listed as “remote.” It is elevated in communities around Belchertown, Tyngsborough, and in parts of Bristol, Norfolk, and Plymouth counties.
The state urges people to remove standing water near their homes or objects that can collect rain because they serve as mosquito breeding grounds.Chelsea Conaboy can be reached at cconaboy@
boston.com. Follow her on Twitter @cconaboy.