TULSA, Oklahoma - Some children may be carriers of bacterial meningitis and not even know it. Doctors say between 10 to 15 percent of school-aged children could be carriers and never get sick, but can infect someone else through direct contact.

Meningitis is an infection of the covering of the brain and spinal cord. Viral meningitis is less severe and makes up 90 percent of the cases.

Then there's bacterial meningitis.

"Life threatening, it can cause a lot of complications even if people live through it, so it's the kind that we're worried about," said Dr. Mitch Duininck of Family Medical Care.

There are two main types of bacterial meningitis -- meningococcal and pneumococcal. The symptoms are the same and may develop over a few hours or a few days.

Dr. Mitch Duininck of St. John Family Medical Care says other types of bacterial meningitis are very rare.

"There are different strains of the bacteria, but even that isn't that important because they cause the same problems, we treat them the same way, they're transmitted the same way," Dr. Duininck said.

Bacterial meningitis must be treated very quickly with antibiotics. Delaying treatment raises the risk of brain damage or death.

It can kill in a matter of days, which was the case in March 2010 in the Oologah-Talala school district. A meningococcal meningitis outbreak killed 7-year-old Andrew Thomas and 8-year-old Shuache Moua.

Five others were hospitalized, but survived, including Jeremiah Mitchell who lost his legs, arms and half his face. Dr. Duininck says the two possible cases of bacterial meningitis this week shouldn't cause panic.

"It just happens, it's horrible when it does and it doesn't mean anybody is doing anything wrong. When you've got a population of a million, million and a half, it comes around sometimes," Dr. Duininck said.

There are two meningococcal vaccines and two pneumococcal vaccines available in the U.S. Those shots protect about 90 percent of the people who receive them. But some people still contract bacterial meningitis even though they've been vaccinated.