[Update: On Monday, several suburban schools and private universities announced closings.]

NEW ROCHELLE, N.Y. — There will be no merrymaking, no buzzing noisemakers and no toddlers dressed up as biblical kings and queens: Purim, the joyous Jewish festival that begins on Monday evening, has been canceled for the congregants of Young Israel of New Rochelle.

Their rabbi has the coronavirus. Their temple was locked last week on the order of the Westchester County health commissioner. And more than 100 families are self-quarantined after one congregant, Lawrence Garbuz, 50, a lawyer from New Rochelle, contracted the virus.

Fear of the spread of the coronavirus — 82 people have been infected in Westchester County, including Mr. Garbuz’s family and neighbors — has upended Purim plans far beyond this small city five miles north of New York City’s borders. The tight-knit nature of the Jewish community, a point of pride, now has a downside: In a world where so many people are interconnected, the risk of transmission rises sharply.

And, as the numbers of the infected climbed over the weekend, Jewish communities that are swept up in an international epidemic considered how to prevent religious life, and Purim, from becoming an incubator of illness.