After upticks in South Brooklyn and two neighborhoods in Queens, coronavirus infections now appear to be growing across wider sections of New York City, raising concern among health experts that the spread of the virus is becoming more widespread and difficult to tamp down.

Last week, the Department of Health had identified six initial clusters, but on Wednesday evening city health officials issued an alert saying that they were now monitoring 10 neighborhoods, including Far Rockaway, South Brooklyn and a portion of Central Queens, where cases are increasing at an alarming rate. The 14-day test positivity rate in all of these neighborhoods have risen above 3%, far above the citywide average, which has been around 1%.

Taken together, the areas account for nearly 28% of new cases citywide over the past two weeks, while representing less than 8% of the city’s overall population, health officials said.

The Department of Health also noted "a slight increase" citywide in visits to emergency departments for those with COVID-like symptoms over the last week.

"This is what expansion of localized community transmission looks like, and is what we would see before a spike in hospitalizations and deaths, and then potentially even wider community spread into more and more neighborhoods," wrote Dr. Denis Nash, an epidemiology professor at CUNY, in an email. "Eventually, and maybe even right now, in many of these neighborhoods, more testing is very likely not going to contain it, even if there is contact tracing."

A spokesperson for the Department of Health did not immediately respond to questions about the latest report.

Citywide, there is now an average of 400 new confirmed cases a day, up from around 250 less than two weeks ago.

On Wednesday, Mayor Bill de Blasio said that around 1,000 city employees, including 400 police officers, had been deployed to targeted ZIP codes. Health officials have focused their efforts targeting their outreach to the Orthodox Jewish community in South Brooklyn, making robocalls and blasting messages on city vehicles in both english and Yiddish, as well as starting inspections of yeshivas. The city is also expanding testing in the affected neighborhoods with the use of 11 mobile testing units as well as rapid testing machines.

But infections are now also rising in areas bordering and near the original 10 cluster sites as evidenced by a list of 7 additional neighborhoods that health officials are monitoring: Williamsburg, Crown Heights (East), Bedford-Stuyvesant (West)/Clinton Hill/Fort Greene, and Hillcrest/Jamaica Estates/Jamaica Hills. In those areas, the 14-day test positivity is now between 2% and 3%. The case growth rate in Williamsburg is more than three times that of the city's rate.

"The fact that it's in a few more neighborhoods adjacent to the other ones is not that big of a surprise," said Dr. Jessica Justman, an epidemiologist at Columbia University. "People do move around a bit."

"The question is what are things going to look like in a week or two weeks from now?" she added.

The increase in positive COVID-19 tests extends beyond what the city has announced. Governor Andrew Cuomo on Wednesday released a list of 20 ZIP codes with a combined daily positivity rate of 5.5%, five times higher than the statewide positivity rate. State health officials use more recent testing data than the city. Based on their analysis, a startling 14 so-called "hotspot" neighborhoods are located in New York City.

Not only that, they touch every single borough: seven in Brooklyn, two in the Bronx, two in Queens, two in Staten Island, and one in Manhattan.

Experts warn against looking at one day's worth of data, which can be subject to fluctuation. The seven-day rolling average is a more reliable indicator.

But the citywide figure has been steadily creeping up. On Thursday, Mayor de Blasio announced during a press conference that New York City's seven-day average positivity rate was 1.52%, up from 1.47% on the prior day.

When asked about the extent of the latest surges, he maintained that the upticks were isolated events. 

“I do think it’s two distinct realities so far,” he said, referring to the "cluster" neighborhoods versus the rest of the city.

The mayor also said that there was no evidence thus far of infections in public schools in the affected areas. Under the current rules, two unrelated infections in a school will force a closure for 14 days. The teachers’ union is pressuring the administration to consider closing 80 schools in covid hotspots.

De Blasio said public schools should remain open, but he acknowledged that broader shutdowns in hotspots are on the table, saying that a decision will be made “as to whether we need to do fuller shutdown in those neighborhoods.”

The surge in cases comes at a precarious juncture in the city's reopening efforts. Public schools began in-person learning with hundreds of thousands of children this week, while restaurants eagerly resumed limited indoor dining on Wednesday. And around 15% of confirmed cases have been linked to those traveling to places with high infection rates. Many experts say that the increase in indoor activity along with the colder weather, which makes the virus more transmissible, will inevitably lead to a second wave or resurgence similar to what is currently occurring in some European countries.

In an email, Dr. Jeffrey Shaman, a public health professor at Columbia who has analyzed the human cost of delaying lockdowns, said that city officials now face a challenging ethical decision.  

"Can the city close down activity in the inflicted areas without doing equivalent harm through the economic disruption?" he wrote.

He added that bringing a "flare up" under control was not an exact science.

"We can shut down, but could the same control be effected by something less severe, given the greater compliance in mask usage? We don’t know the answer to this."