For the past nine months, Princeton University in New Jersey has been trying to halt an outbreak of bacterial meningitis in its students without success. So it's going to offer students a vaccine that's not yet approved for broader use in the US.

Since bacterial meningitis is a serious infection of the brain and spinal cord that can cause brain damage and death, having it on campus is no small matter.

The situation in Princeton, where six students and a visiting student have fallen ill, got us thinking — why do meningitis outbreaks seem to happen most often on college campuses? We asked Dr. Thomas Clark, a meningitis expert at the Centers for Disease Control and Prevention, to tell us why that happens. Here's the conversation, edited for length and clarity.

Why do meningitis outbreaks seem to happen so often on college campuses?

Well, we know that adolescents and young adults are at higher risk for meningococcal disease overall. But meningitis occurs in all age groups and it occurs in all states in the U.S. So every day there's a case or two. Most cases are sporadic; they just happen individually and that's it. In fact, 98 percent of cases are sporadic.

But outbreaks do occur. And it really has to do with sustained patterns for social interactions among college students. Really close contact, living in dorms are especially known to put kids at risk.

It's transmitted either by close contact or face-to-face prolonged contact. It's carried through large respiratory droplets or oral secretions. So really, it's not casually transmitted. It requires pretty close, fairly intimate contact.

So it could be transmitted through a kiss?

Well, maybe French kissing. But that's not the only way it's transmitted. If you live in close quarters, the roommate is at very high risk to get infected. We give preventative antibiotics to people who are around an infected patient.

But it really requires direct contact with people. You'll find a little bit of information out there in some experimental studies that if you put the bacteria on surfaces, a fraction of them will survive for a few hours, but we don't think that's an efficient way for transmission.

Other than college campuses, where do meningitis outbreaks tend to occur?

It often ends up being an institution. So a college campus, elementary schools and high schools, prisons. Outbreaks are more likely to occur in places with lots of people in close contact.

What's unique about the outbreak in Princeton?

When you hear about meningitis outbreaks, really what you're talking about is a type of bacteria called Neisseria meningitidis or meningococcus — they're the same thing. But we divide those bacteria into strains or serogroups. The vaccines we recommend routinely cover four serogroups — A, C, W-135 and Y. Traditionally, outbreaks are seogroup C — and cases tend to occur in a short period of time very quickly and closely, back-to-back.

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