BOSTON — Doctors evaluating Teresa Heinz Kerry, wife of U.S. Secretary of State John Kerry, reported improvement in her condition Monday, according to the State Department, but few details were being disclosed about her illness.

Heinz Kerry, 74, who is also heir to the Heinz ketchup fortune, was flown to Massachusetts General Hospital in Boston on Sunday after first being brought by ambulance to a hospital on the Massachusetts island of Nantucket, where the couple has a home and often spends time during the summer.

Heinz Kerry showed symptoms consistent with a seizure, said a person in close contact with the family who was not authorized to speak publicly about Heinz Kerry’s condition and spoke on condition of anonymity.

Doctors upgraded Heinz Kerry’s condition from critical to fair Monday after conducting tests and she was undergoing further evaluation, Glen Johnson, a spokesman for Kerry, said in a statement.

“The family is touched by the outpouring of well-wishes,” Johnson added.

Kerry was at the hospital with his wife Monday.