Suffolk County Department of Health Services was notified of the case by the hospital June 8. Health officials then notified the school district.
Citing privacy laws, the department could only confirm the case and that the person, a student at East Islip High School, remains hospitalized.
The school district on Monday notified parents, students and faculty via email and telephone calls.
The message was "to alert the school community to a confirmed case of meningococcal disease at East Islip High School," the district's website said in a posting.
Grace Kelly-McGovern, the health department spokeswoman, said bacterial meningitis is most often serious and can be life-threatening. Viral meningitis, while serious, is rarely fatal to those with normal immune systems, according to the Centers for Disease Control and Prevention.
Meningitis is caused by the inflammation of the protective membranes covering the brain and spinal cord known as the meninges, the agency's website said. Typically, the inflammation is from an infection of the fluid surrounding the brain and spinal cord.
Bacterial meningitis is contagious, with bacteria spreading through the exchange of respiratory and throat secretions, according to the CDC.
The family of the East Islip student has been treated to help prevent the spread of the disease, Kelly-McGovern said.
Annually, between 2003 and 2007, an average of 4,100 cases of bacterial meningitis were reported with 500 deaths, the CDC reported.