“We have seen a huge spike in positive results just in the last 48 hours,” Mr. Eichenstein said on Wednesday. “However, at this point, it is unclear if the spike is due to greater testing or whether the virus has actually hit Borough Park in greater fashion.”

On Wednesday afternoon, a crew in protective jumpsuits could be seen cleaning the urgent care center in Borough Park.

Joel Bernat, an executive at the cleaning company, Disinfect New York, said it had been called to Asisa Urgent Care twice in the last two weeks after patients tested positive for the coronavirus.

He said the city should have issued stronger warnings about the coronavirus two weeks ago, and that the neighborhood was at risk because its residents “live very close together.”

A group of patients, some wanting to be tested, stood on the sidewalk outside the clinic. One woman cradled an infant while another, wearing a mask, took the baby’s temperature. One man held his lapel over his mouth, while others shivered, coughed or blew their nose.

“They won’t even let me find out if I need a test,” said a man who gave only his first name, Chaim. He said he was 72 years old and had a dry cough. “Everything is so vague. Nobody knows anything.”

A gaunt man who gave his first name, Jacob, and said that he was 37, said that he suspected that he was infected with the coronavirus.