With coronavirus cases surging, some experts are urging or weighing widespread school closures around the region, while other health officials and districts are pushing back in favor of continuing in-person instruction.

One day after the Philadelphia School District scuttled its plans to start bringing staff and students back to the classroom this month, officials in Montgomery County said Wednesday they are weighing a two-week shutdown for all schools.

The state’s largest teachers' union called on districts with high levels of virus transmission, including around Philadelphia, to revert to virtual programs.

And experts at the Children’s Hospital of Philadelphia, one of the region’s prominent voices on the virus, warned Wednesday of a “catastrophic situation” building and urged all to shut down classroom instruction as soon as next week.

“We are sort of at the collapse of these plans” for school reopenings, said David Rubin, director of the CHOP PolicyLab. The research team on Wednesday advised schools around Philadelphia to revert to virtual programs, at least for older grades, starting Monday and continuing through New Year’s.

The number of coronavirus cases has been rising in and around Philadelphia — Pennsylvania again surpassed 4,000 new cases, setting a daily high for infections — as have hospitalization rates. Health officials have asked residents to avoid social gatherings, as they seek to avert more stringent shutdowns.

Pennsylvania isn’t publishing data on school outbreaks, making it difficult to assess to what extent the virus may be spreading in schools. In New Jersey — which has more than 580 school districts — the state has reported 36 school outbreaks, with 146 linked cases.

Experts say if the virus is spreading rapidly, it’s more likely to enter — and spread within — schools, making community transmission rates important.

Higher transmission rates also place staffing pressure on school districts, as increasing numbers of employees are forced to quarantine after being exposed to the virus. “It’s the staffing that’s killing us,” said Jim Scanlon, superintendent in the West Chester Area School District, where 15 employees at the middle-school level are under quarantine.

The district, which is offering part-time in-person instruction, isn’t currently planning to go virtual.

Pennsylvania’s health secretary, Rachel Levine, said earlier this week that the state did not plan to mandate school closures as it did when the pandemic emerged in the spring.

Guidelines issued by the state earlier this year advise schools pre-K to 12th grade in counties with “substantial transmission” — based on the rate of infections per 100,000 residents or the rate of people who test positive for the virus — to only offer virtual instruction.

But not all districts are following those recommendations, said Rich Askey, president of the Pennsylvania State Education Association.

Among the counties that fell into the “substantial” category in the week ending Nov. 6 were Bucks, Delaware, Montgomery, and Philadelphia, according to the state.

“It is absolutely unacceptable for any school district to disregard the advice of medical professionals and scientists during a pandemic and put the safety of students, staff, and their families at risk,” Askey said Wednesday, calling on districts to follow the state thresholds.

Even as some county health officials report low rates of in-school transmission, given how widely the virus is spreading, Rubin said it’s time for schools to consider closing.

While most infections of children and teachers appear to be occurring outside of school, there is “increasing evidence” that the virus is being transmitted in schools around the area, Rubin said. He said there may be more in-school transmission occurring than is known, because contact tracers haven’t been able to keep up with the growing caseload.

Officials in Montgomery County — where schools were the first to close in March, triggering a two-week shutdown that stretched into the spring — are also concerned. The board of public health will hold a special meeting Thursday to consider ordering all schools in the county to revert to virtual learning for two weeks, beginning Nov. 23, said spokesperson Kelly Cofrancisco.

In a letter to families Wednesday, the Lower Merion School District said it was shutting down bus service for the rest of the week due to an outbreak among its transportation staff. It also said it was reevaluating how it would provide instruction going forward.

“Unfortunately, our schools do not exist in a bubble and circumstances in our surrounding community are such that we need to change our plans," said Superintendent Robert Copeland. He said the district had taken note of the CHOP recommendations and had “not yet made a decision about our instructional model for next week, but will advise families" before Friday afternoon.

Other counties — and school districts — indicated they may not change course. The Chester County Health Department, which also serves as the health department for Delaware County, said Wednesday that it “supports schools continuing with their instructional model plans.”

Bucks County Health Director David Damsker said closing schools “may sound like the knee-jerk reaction thing to do, but I think it’s a mistake.”

“We’re not recommending shutting down Giant and Target and Home Depot because they’re essential for society," he said. "Schools are essential for society.”

A number of school leaders said they didn’t see the logic in switching to virtual instruction when they hadn’t yet been forced to close any individual buildings due to coronavirus cases.

“We’re going to do our best to remain open for the kids,” said Maureen Reusche, superintendent in the Haverford Township School District, which is offering hybrid in-person and online instruction to students.

While the district has seen 19 cases of the virus among students and staff since reopening in October, none have been linked, Reusche said.

“Why is closing schools the number-one mitigation strategy?” she said.

In Delaware County — which is seeing the second-highest rates of infection in the region behind Philadelphia — “we all have concerns over the increasing rate of community transmission, especially the effect on hospital capacity,” said Lee Ann Wentzel, superintendent of the Ridley School District. But Wentzel said her district is staying put for now, with students able to attend school part-time in a hybrid model. (Roughly 30% of Ridley students have chosen to learn completely virtually.)

“The value of in-person learning is so important for children," Wentzel said. "The hard part for us as educators is that this community transmission isn’t occurring in schools, but you’re asking children to bear the burden because community transmission is so high.”

While many area public schools delayed in-person starts to the school year — some citing guidance from CHOP — some private schools have been instructing children in classrooms throughout the fall, including the Archdiocese of Philadelphia. Spokesperson Kenneth Gavin said Wednesday that elementary schools will continue to operate full-time, and secondary schools in a hybrid model.

Many schools have faced pressure to open in person from parents who say their children are languishing at home — and who are also struggling to manage their own work schedules.

While there is debate about whether children — who tend to experience milder infections — would be safer in school than in other settings, CHOP’s Rubin said, “we need to get control of this." Some hospitals could be overrun if the virus isn’t contained, he said.

Despite his recommendation they close, Rubin allowed it might make sense for schools to continue to offer in-person learning to younger children or special-needs students. And while CHOP is recommending that schools stay closed for at least the rest of the year, those in areas with lesser hospitalization rates could bring some students back in early to mid-December, Rubin said.

Some districts had already planned to remain virtual even before the recent surge in the virus.

Camden School Superintendent Katrina McCombs said remote instruction is the best option until there is a vaccine. Her district has been virtual since the school year began and plans to continue that way until at least Feb. 1.

“It’s the most stable option right now,” McCombs said “Daybyday you’re on edge.”

Staff writer Melanie Burney contributed to this article.