A measles outbreak in a New York suburb has sickened scores of people and stoked long-smoldering tensions between the ultra-Orthodox Jewish community and the secular world at large.

A measles outbreak in this suburban New York county has sickened scores of people and alarmed public health experts who fear it may be a harbinger of the growing influence of the anti-vaccine movement. But it has also intensified long-smoldering tensions between the rapidly expanding and insular ultra-Orthodox Jewish community and secular society.

The authorities here in Rockland County have traced the spread of measles to ultra-Orthodox families whose children have not been vaccinated.

And so some residents say they now wipe public bus seats and cross the street when they see ultra-Orthodox Jews. Hasidic leaders said they feared not only a rise in anti-Semitism but an invasion of their cloistered community by the authorities under the guise of public health.

Officials took the extraordinary step of announcing a state of emergency, barring unvaccinated children under 18 from public places, including restaurants, shopping centers, houses of worship and schools.

“They did it to themselves,” Ms. Wingate said, referring to the Hasidic people who have refused to vaccinate. “But I feel terrible for everyone.”The emergency order has emerged as a flash point in a continuing clash in Rockland County, a collection of five towns just northwest of New York City with a combined population of more than 300,000 people.

About 31 percent of the population is Jewish, according to the state, and includes one of the largest concentrations of ultra-Orthodox Jews in the country. The surge in the ultra-Orthodox population has been driven in part by Hasidic families from Queens and Brooklyn, where there has also been an outbreak.

While those tensions were once buffered by yeshiva walls and eruvim, the symbolic perimeters around Hasidic enclaves, the outbreak of measles, which is highly contagious, cannot be kept to such boundaries.

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“I think that for the most part people have been just annoyed — in certain parts of the county you can’t buy a house or can’t sell your house,” said Jessica Finnegan, 32, who was pushing her eight-month-old son, Kieran, in his stroller through a Target store in Spring Valley. The store had been previously identified by officials as one place where people may have been exposed to measles. The outbreak of the disease began in October.

More than 17,000 doses of the measles-mumps-rubella vaccine have been administered in the county in the past 26 weeks, and the county’s public health campaign included doctors as well as rabbis exhorting the importance of immunization. But the outbreak has persisted. As of Friday, there had been 157 confirmed cases of measles in the county since October.

The measure aimed at unvaccinated minors was a last resort, according to medical experts.

The anti-vaccine movement is rooted in a belief that the inoculations are linked to autism, a claim that is not medically substantiated.