The boy - identified as Sean Weisse by a family member - was taken off life support Sunday, three days after being hospitalized with symptoms of fever, nausea and a sore throat, said Claudia Hutton, a health department spokeswoman.
"There is no reason to believe the hospital did anything except provide the best medical care," Hutton said. "Any time a child dies unexpectedly, it is of great interest to us."
The probe is not aimed at Stony Brook's pediatric intensive care unit, the subject of state scrutiny for past quality of care issues, Hutton said. She said a hospital inspection team was investigating it as "an adverse event."
Stony Brook staffers have conducted blood and spinal fluid tests but have not determined the cause of death, Hutton said, adding that doctors believed the fatal illness was viral. More tests are scheduled on the spinal fluid taken at St. Catherine of Siena Medical Center in Smithtown, where the boy was first taken after becoming ill, Hutton said.
There will be no autopsy at the family's request, Hutton said.
"Mysterious deaths do happen and there are times when you cannot get all the answers that you want," Hutton said. "I don't know how certain, in the end, a cause of death will be."
Sean, a third-grader at Park View Elementary School, is scheduled to be buried Thursday after a funeral Mass at St. Joseph's Roman Catholic Church in Kings Park. The boy's parents, Steven and Kelly Weisse, asked that donations be made to the Special Education Parent Teachers Association of the Kings Park Central School District. They declined interview requests.
Health authorities sought to assure the public that Sean did not die from a reaction to a flu vaccine shot last week, a claim posted this week on several Internet message boards and blogs.
Hutton said the boy was given a regular seasonal flu shot in a private physician's office, but results from blood and spinal fluid tests show that it is "extremely unlikely" that the vaccination caused his illness later.
"There is always a very remote chance, but it is so remote that it is almost a scientific certainty that it is not vaccine-related," Hutton said. "It is just a very sad family tragedy."
The Centers for Disease Control and Prevention said fatal reactions to flu shots are rare.
At a wake in Kings Park Wednesday night, friends and family remembered a smiling boy who loved skateboarding. His skateboard was placed near his coffin amid flowers and photographs.
"Every picture he has a big grin on," said Kerry Leo, a family friend from Kings Park.
Counselors were on hand this week at Park View Elementary to help students and faculty, said Susan Agruso, superintendent of the Kings Park Central School District. "This is a profoundly sad time for our community," she said. "Our sincerest sympathies go out to the student's parents, family and friends."