CNN)— To contain a measles outbreak, a newly infected person has to work in tandem with state and local health authorities, providing information on when their symptoms began and whom they may have exposed during the nine days they are contagious.

Most people do. Then there are those who refuse.

Just last week in Rockland County, New York, which has been battling a persistent outbreak of measles in the Orthodox Jewish community for six months, a contagious person stopped cooperating with local investigators.

“[They] notified us that they were at a Target in Spring Valley, New York,” said John Lyon, director of strategic communications for the Office of County Executive in Rockland County, New York.

“But then they stopped returning our phone calls, wouldn’t pick up the phone, wouldn’t help us narrow down the time they were there,” Lyon said.

That’s critical information, he said, because measles can live in the air and on surfaces for up to two hours. By narrowing the time of exposure in a public place, he said, officials can reassure fearful residents and keep that “mother with the 2-month old from worrying.”

“She can say, ‘OK, I went to the store, but I wasn’t there at that time, so my baby’s OK,’ ” Lyon said.

In this case, however, the county had to issue a warning of possible exposure over a two-day period, March 10 and 11, Lyon said, “needlessly worrying” that mom and other residents.

That was just one example. Refusing to cooperate was happening so often, Lyon said, that the city said “enough was enough” and took the unusual step Wednesday of banning unvaccinated people under age 18 from going to public places

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