Local, state and national health experts are baffled as to how a rare and deadly strain of meningitis killed four people and infected eight others in South Florida since December, an unprecedented outbreak in the United States.

The cases of the W135 strain of meningitis were disclosed Wednesday by Miami-Dade health officials. On Thursday, they were recommending vaccinations for those in high-risk groups –mainly those living in close and crowded situations such as college dorms or military barracks.

"We're stumped," Dr. Vincent Conte, senior physician at the Miami-Dade Health Department, said Thursday. "There doesn't seem to be any pattern. We have cases in North Dade, South Dade, East Dade and West Dade. There's no cluster. It's everywhere."

"We've never had a transmission like this in the United States," said Amanda Cohn, an Atlanta physician with the U.S. Centers for Disease Control and Prevention who specializes in meningitis.

The most recent reported case was earlier this month, a British tourist who died April 7. Though the county would not reveal names or specific details about any of the cases beyond age or gender, family members verified that the victim was Jade Thomas, a schoolteacher from Nottingham, England. She died while on vacation in Florida to celebrate her 26th birthday.

People in South Florida kept their cool despite news that the W135 strain of meningitis can have a mortality rate as high as 20 percent. Local family doctors reported only a trickle of calls from families, mostly asking if their vaccinations were up to date.

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