Eight Marine recruits who were hospitalized in isolation at Naval Medical Center San Diego overnight for treatment of meningitis were released early Friday after medical tests for the disease came back negative, a center spokeswoman said.

The recruits, whose names and hometowns were not released, were admitted to the center’s emergency room around 9 p.m. Thursday and released back to Marine Corps Recruit Depot San Diego Friday morning, said Sonja Hanson, a public affairs officer for the medical center.

San Diego Marine Corps Recruit Depot during 2010 visit by Secretary of Defense Robert Gates.

According to Hanson, the recruits all presented similar symptoms, including some common with an upper respiratory infection. Five appeared to have more severe cases and were given medication to prevent illness, she said.

While the Marines were in isolation rooms within the center, tests were run to determine whether they had bacterial or viral meningitis.

Meningitis attacks the protective membranes that cover the brain and spinal cord. Viral meningitis is generally less severe, while the bacterial form of the illness can result in brain damage, hearing loss or learning disabilities, according to the Centers for Disease Control and Prevention.

The tests conducted overnight turned out negative for both forms of the disease, Hanson said.

A 2012 CDC report said that from 2006 to 2010, 26 confirmed cases of meningitis were found among U.S. military members. Five of those cases were fatal.

Incidences among 17- to 19-year-old basic trainees and among U.S. Marines were significantly higher than among older trainees and those in other branches of the military, according to the report.

Last month, two people in San Diego County not affiliated with the local recruit depot died from meningitis — Patrick Henry High School freshman Jewelean Pimentel and 52-year-old Santee resident Jackie Lerma Billings.

Pimentel had the bacterial form of the disease and died at Rady Children’s Hospital two days after she came home from school complaining about a headache, her family said.

According to county heath officials, Billings died from a different, milder strain of meningitis than the one that took Pimentel’s life. Billings family said she went to the hospital to treat what she thought was the flu and fell into a coma two days later.

— Çity News Service