STORRS — The University of Connecticut has banned residential students from attending off-campus gatherings over the Halloween weekend and into next week.

Residential students caught violating the rule will be referred to the university’s Community Standards office by state police, UConn Dean of Students Eleanor Daugherty said Friday.

That decision comes as the state university saw the largest single-day increase in COVID-19 cases since late September.

Testing results released Friday showed 15 new cases in and around the Storrs campus. Nine of the new cases were among students living off campus, a 5.6 percent positivity rate among those students.

Three of the new cases were among residential students living at Storrs, and three were among university employees and affiliates.

Fifteen students are in isolation on campus after testing positive for the disease or showing symptoms, according to UConn’s data.

The spike of new cases off-campus has UConn officials concerned because the cases are not associated with a seminal event, such as a college party.

“There is no indication that the new cases are interrelated, meaning they don’t live in close proximity and are not known, for example, to have attended the same social gathering. Rather, they are scattered,” said Stephanie Reitz, a spokeswoman for UConn.

Testing of campus residents and the Storrs wastewater has not revealed a comparable spike on campus, Daugherty said.

The new cases come as the entire state on average has crossed the threshold into red alert zone of more than 15 cases per day per 100,000 over a 14-day period.

The spike follows several weeks when UConn’s active caseload in and around Storrs has declined, after cases there led university officials to issue a handful of quarantine orders for dorms and one off-campus apartment complex earlier in the semester.

“This is the reality of COVID-19 as it surges throughout the state of Connecticut, our country, and our world,” Daugherty wrote in a letter to the community.

Yale University is also reporting a spike in coronavirus infections, with 21 new cases reported Wednesday (the most recent daily test numbers available), bringing the university’s cumulative total for the semester from 88 to 109. Of those cases, 35 were reported in the previous seven days as of Wednesday, Yale’s data shows.

Those figures come as New Haven, all of its outlying municipalities and a swath of central Connecticut have all been placed in the orange alert zone.

New Haven Mayor Justin Elicker said Thursday Yale cases have not been included in the city’s totals. “The reason for that is a lot of the students have out-of-state addresses,” Elicker said.

In Fairfield, Sacred Heart and Fairfield universities have issued similar warnings about partying over the Halloween weekend.

Sacred Heart officials doubled down on that warning Friday.

“We want you to celebrate and have fun, but please do it safely,” the university’s coronavirus team told students in a message.

The school reported 14 new cases as of Thursday — eight on campus, and six off campus, all among students. The number of active cases stood at 58, down from 62 just 24 hours before.

Fairfield University reminded students Pennsylvania and Massachusetts have both been added to the state’s travel advisory list, and noted students who need to quarantine for 14 days after traveling to one of those states cannot do so on campus.

The school reported three new cases of COVID-19 as of Thursday, all among students, bringing the active caseload to 39 — which includes four active cases among faculty and staff.

Quinnipiac University in Hamden reported nine new cases Friday, 36 within the past seven days. The university has recorded a cumulative 75 confirmed COVID-19 cases so far this semester.

Southern Connecticut State University in New Haven reported seven new cases between Sunday and Tuesday, bringing the school’s cumulative total to 59 cases.

The University of New Haven in West Haven, reported eight new cases as of Friday, bringing the number of active cases there to 19, all among students.

The University of Saint Joseph in West Hartford reported five new cases in the past week— one among employees, four among students.

Central Connecticut State University in New Britain reported one new case Thursday, a member of the school faculty or staff. The university currently has four students in quarantine and one in isolation, according to its database.

Connecticut College in New London reported four new cases this week, three students and one employee. The new cases bring the school’s active cases to seven, three students, four employees.

Eastern Connecticut State University in Willimantic reported four new cases, all among commuter students, this week. As of Friday, 37 students are in isolation or quarantine both on and off campus, the school’s data shows.

Trinity College in Hartford reported six new cases this week, brining the school’s caseload to eight — six students and two employees.

Wesleyan University in Middletown reported three new cases in the past week, bringing the school’s active cases to six. Those include four employees and two students.

The school also elevated its COVID-19 alert status to yellow from green. In a message posed to Wesleyan’s website, the school said that was taken as a precaution given the rise of cases in Middletown and the state as a whole.

“As a result, Wesleyan has asked students to avoid all unnecessary travel into the surrounding community,” the message read. “Because the positivity rate on campus remains quite low, no other campus restrictions are being imposed at this time.”