Some inexplicable things come out of our nation’s capital. Occasionally, similar puzzlements emerge elsewhere in the nation.

A current one is the developing outbreak of preventable measles that’s become so serious now that federal officials have threatened some with unusually restrictive travel bans.

Some of us were unaware that such a federal Do Not Board List exists for civilians who have nothing to do with suspected terrorism.

But it does. And according to the Washington Post, health officials in five states have contacted the Centers for Disease Control and Prevention about banning travel by some citizens suspected of being in the 21-day incubation period for measles infection.

The five states are the usual mostly coastal suspects for urban trouble — California, New York, Illinois, Washington and Texas.

This year has produced the most U.S. measles cases in a quarter-century. Most domestic cases develop from among the 15 to 20 percent of Americans who are unvaccinated returning home from such heavily-infected places as Ukraine, Philippines and Israel.

Such outbreaks have become more common with the growth of rapid, long-distance air travel and the spread of an anti-vaccine movement around the globe.

New York City is the worst affected domestic location this year. Officials there closed schools that refused to keep unvaccinated children at home and issued mandatory vaccination orders with four-figure fines in some neighborhoods.

A travel ban is less restrictive than quarantine or isolation. It’s rarely used because such a government restriction is so politically charged.

It was designed after a Georgia man with drug-resistant tuberculosis flew to Europe against health officials’ advice in 2007.

Just mention of a travel ban is often enough. “The deterrent effect is huge,” said Martin Cetron who tracks disease outbreaks with the CDC.

“If all those things are not enough to convince somebody,” Cetron added, “then the last thing we do is contact the Department of Homeland Security, give them the appropriate identifying information, and someone gets put on the list. And if they were to go to the airport, they’re not issued a boarding card.”

This year, in fact, every one of those contacted about the ban voluntarily cancelled their trip. And the CDC wrote the airlines requesting fare refunds for cooperative travelers.

“It’s just plain common sense,” said Lawrence Gostin, a health policy expert at Georgetown University, “that if you have an actively infectious individual, they should not get on an airplane.”