An outbreak at an Oxford County paper mill helped fuel Maine’s largest spike in new COVID-19 cases in more than two weeks on Friday and the Sanford school district moved its high school and regional technical center to full distance learning after someone connected to the high school tested positive.

The daily tally of 46 new cases included 15 cases in Oxford County, where the outbreak at ND Paper in Rumford grew from four cases on Tuesday to 16 as of Friday, the Maine Center for Disease Control and Prevention said. The state recorded 51 cases on Sept. 2 and 55 cases on Aug. 28, but since Sept. 3, daily new cases have mostly been in the 20s or 30s. The seven-day daily average of 31.7 is the highest since July 2.

York County, the site of numerous outbreaks, reported eight new cases Friday, and Cumberland County had five. There were no additional deaths.

The superintendent of schools in Sanford, which is in York County, moved the high school and the Sanford Regional Technical Center to distance learning for all students beginning Monday after “an individual associated with Sanford High School recently tested positive.”

“There is a possibility that other staff or students came in contact with this individual and therefore may have been exposed to the virus,” Superintendent Matt Nelson said in a letter posted on the school department website Friday afternoon.

Sanford, like all districts in York County, had been in the state’s yellow category indicating that schools should employ a hybrid schedule combining remote and in-person learning. Nelson’s statement said the high school and technical center would move to the red category in which all students learn remotely.

He said the district’s middle school for grades 5-8 will continue in the red category with a possible return to in-person learning on Sept. 28. Grades K-4 will continue with a yellow hybrid model with students attending two days a week in two groups.

“Please understand this is a fluid situation,” Nelson said. “We will continue to assess and adjust accordingly.”

In another development Friday, a Waterville hospital quarantined 10 members of its healthcare staff after they were exposed, directly or indirectly, to a patient who later tested positive for COVID-19. Inland Hospital, part of the 10-hospital Northern Light Health network, disclosed the quarantines in a short statement posted on the network’s website late Friday afternoon, but declined to share further details, including how so many hospital workers came to be potentially exposed.

Since the pandemic began, 5,005 cases of COVID-19 have been recorded in Maine, including 138 deaths.

On Thursday, the Maine CDC reported an outbreak at the Portsmouth Naval Shipyard in Kittery, with 18 cases, 13 of them Maine residents.

The outbreak is believed to be related to a commuter van from Sanford, where seven of nine people who used the van contracted COVID-19.

Gary Hildreth, spokesman for the shipyard, said in a statement that “those in the vanpool did not wear cloth face masks while commuting to and from work.”

The Maine CDC reported that 16 of the 18 people in the shipyard outbreak were employees, while the other two were close household contacts of employees. Of those who have fallen ill in connection with the shipyard outbreak, 13 are from Maine, four from New Hampshire and one from Massachusetts.

Other outbreaks reported Thursday include three cases at Baker Company in Sanford and four cases at Buffalo Wild Wings in Auburn.

And outbreaks in York County at social clubs in Sanford have grown to include a new outbreak – first reported Wednesday – of four cases at the Elks Lodge. At previously-reported outbreaks, case counts have grown to 12 at the Sanford American Legion, 10 at the Lafayette Social Club and 10 at the Sanford VFW.

Dr. Nirav Shah, Maine CDC director, said in an interview with the Press Herald that social clubs are licensed similar to restaurants, but that they are a “hybrid” with similarities to bars and restaurants. Bars remain closed in Maine because of their links to super-spreading events in other states, while the state permitted restaurants to reopen this summer after being shuttered this spring.

“Structurally, social clubs are a lot more similar to an Applebee’s,” Shah said. “They are viewed as restaurants that happen to serve alcohol, that’s how they’re licensed and that’s how we think of them.”

He said the social club outbreaks are an example of how higher levels of disease within a community can lead to outbreaks.

“It raises the concern that what we are seeing could lead to exponential growth,” Shah said, referring to not just the social club outbreaks but outbreaks throughout York County. “We could have an explosion of cases, that’s why this is deeply concerning.”

While an Aug. 31 funeral reception at the Sanford American Legion is believed to be the source of that outbreak, the others are still under investigation. Shah said he does not know to what extent the social clubs have followed the rules, which include 6 feet between tables and customers, restrictions on how many people can be in the restaurant, typically 50 or fewer, and requiring employees to wear masks and customers to wear masks when they are not sitting down eating or drinking.

If the rules are followed that would reduce some risk, but not eliminate all risk from indoor dining, Shah said.

The U.S. CDC recently released a study that showed a correlation between restaurant dining and those who had contracted COVID-19. Those who had contracted COVID-19 were twice as likely to have eaten at a restaurant within the previous 14 days compared to those who did not dine out.

Dr. Michael Mina, an assistant professor of epidemiology at Harvard University, said he sees the U.S. CDC restaurant study as an example of the types of populations being surveyed rather than saying much about the inherent risks of restaurants.

“Those who are going to restaurants (indoors) during a pandemic are probably also more willing to engage – in the context of COVID-19 – other risky behaviors,” Mina said.

He also said while he doesn’t know about social clubs in particular, places where customers socialize more like a bar, with people wandering around the facility and mixing with other groups, are more risky than a traditional sit-down restaurant. Fewer people socializing means the risk of transmission is lower, he said.

“At restaurants, people are sitting at a particular table, it’s more organized and there’s not as much mixing among groups of people as there would be at bars,” Mina said.

Hospitalizations for COVID-19 have been gently but steadily increasing over the past two weeks at medical centers in York and Cumberland counties, with Southern Maine Health Care Medical Center in Biddeford seeing its busiest week since late June.

SMHC, York County’s largest hospital, had an average of three confirmed COVID-19 inpatients for the week ending Thursday and 1.1 the week before. This trend, which followed multiple outbreaks in the area, followed two months of relative quiet, with only an occasional inpatient. York Hospital has had a COVID-19 inpatient each day since Monday after going 12 days without any.

Maine Medical Center, which has cared for nearly half of all those hospitalized with COVID-19 statewide since the start of the pandemic, had its busiest week since early July, with an average of 5.1 COVID-19 inpatients per day, and 3.4 the previous week. Its average daily patient load had fallen to under 2 in the second half of August.

Portland’s other major hospital, Northern Light Mercy Hospital, had one such a patient each day this past week, after going 22 days without one. But hospitals in the rest of the state were generally quiet, including major hospitals in Lewiston, Bangor and Augusta.