A Suffolk County man in his 70s is hospitalized with West Nile virus, the third Massachusetts resident to be diagnosed this year with the mosquito-borne disease, state health officials said Tuesday.

The two other cases included a Norfolk County man in his 70s reported by the Department of Public Health last week, and a Middlesex County woman, also in her 70s, a month ago.

Health authorities did not disclose details of the Suffolk County man’s medical status.

The department warned residents that mosquitoes will continue to pose a danger until the first hard frost.

“It is especially important for individuals over the age of 50, and those that [have compromised immune systems] to continue to avoid mosquito bites by using repellent, using clothes to reduce exposed skin, and reducing outdoor activity between dusk and dawn.’’ Dr. Catherine Brown, state public health veterinarian, said in a statement.

The virus can infect people of all ages, but people older than 50 are at higher risk for severe disease. Most people who are infected will have no symptoms. When present, symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

Last year, there were 10 cases of West Nile infection reported in Massachusetts.

More information can be found on the Arbovirus Surveillance Information webpage at www.mass.gov/dph/mosquito or by calling the Department of Public Health Epidemiology Program at 617-983-6800.

Kay Lazar can be reached at kay.lazar@globe.com.