New York City officials announced on Tuesday a significant uptick in the citywide daily rate of positive virus tests, which was in part attributable to a rise in cases in nine ZIP codes in Brooklyn and Queens — some in predominantly Orthodox Jewish communities.
“That is cause for real concern,” the mayor said.
The uptick comes at a particularly crucial moment, as the city tries to fully reopen schools and introduce indoor dining this week.
Over the past two weeks, the cases in the nine ZIP codes account for 25 percent of the city’s virus cases, despite the fact that the population in those areas make up only 7 percent of the city’s population, according to Dr. Dave Chokshi, the city’s health commissioner.
Many of the new cases in recent weeks — at least 1,600 — have taken place in what city officials are calling the “Ocean Parkway cluster,” named after the boulevard that runs from the bottom of Prospect Park south to the ocean.
The cluster was detected last month as case rates rose in Borough Park, a predominately Orthodox Jewish neighborhood where mask-wearing has been a rarity. In interviews last week, several Hasidic men who live in Borough Park said that many members of their community thought the neighborhood had a degree of herd immunity because of how hard-hit it was in March and April.
“There is still no evidence of herd immunity in any community,” Dr. Chokshi said on Tuesday.
City officials said they believed that mask-wearing had become more common in and around Borough Park after renewed efforts in recent days by public health officials to secure cooperation from community leaders.
“I really felt that we had turned the tide,” Dr. Mitchell Katz, who heads the city’s public hospital system, said of increased mask-wearing.
As part of new enforcement measures, the city will move to fine anybody not wearing a mask, the mayor said. “That will be starting on a large scale today,” he said.
Also, nonpublic schools and child care centers will be forced to close if they do not adhere to safety measures.
The citywide positivity rate has major implications for the public school system. Under current guidelines, classrooms will close if the test positivity rate exceeds 3 percent over a seven-day rolling average. Mr. de Blasio said on Tuesday that he would not seek to change those guidelines to target specific areas that had seen an uptick.
The mayor said that the current seven-day average was 1.38 percent, and that the city had not seen an increase in cases in schools in the nine ZIP codes in question.
If schools are forced to close, it could take weeks for them to reopen, according to the city’s health officials.
“The goal is to be under 3 percent in a way that is consistent,” Mr. de Blasio said.
But he cautioned that the city was not yet near that point.
Plans to introduce indoor dining in the city on Wednesday will not be affected, the mayor said.
Early last week, city health officials warned residents of several areas — including Gravesend, Borough Park and Midwood in Brooklyn — that strict lockdown measures would be enacted if they did not see a larger effort to follow coronavirus safety measures.
Last week, the city health department threatened to ban gatherings of more than 10 people if improvement was not seen quickly. That restriction has not been implemented so far.