The University of Minnesota has paused its football program and canceled Saturday's game against Wisconsin due to a "sudden increase" in COVID-19 cases, officials said.

Nine student-athletes and six staff members have tested positive for COVID-19 in the last five days, officials said Tuesday. The program is also awaiting confirmation of additional presumptive positive tests.

The numbers marked a "sudden increase in positive cases," Dr. Brad Nelson, the department's medical director, said in a statement. The pause "will allow the team to focus on stopping the spread of the virus," he said.

The cancellation marks the first time Minnesota and Wisconsin won't play in 113 consecutive years, ending the longest uninterrupted series in Football Bowl Subdivision history, according to ESPN.

Saturday's game at Wisconsin will not be rescheduled, per Big Ten policy, and will be ruled a no contest.

Minnesota officials said they hope to be healthy enough to play Northwestern on Dec. 5.

With holiday travel approaching, a top White House coronavirus official warned against a false sense of security that a negative COVID-19 test might provide.

"Please remember that a negative test today does not mean you will be negative tomorrow or in a few days afterwards," Adm. Brett Giroir, assistant secretary of health at the Department of Health and Human Services, said on a call with reporters Tuesday. "We know that a single test can provide false senses of security. You still have to wear your mask and everything else."

"If you're negative today, you could be positive by Thanksgiving or Friday," he continued. "You can get it while you're traveling on vacation."

Giroir confirmed that the Trump administration is considering shortening the recommended coronavirus quarantine time from 14 days to 10 days, complemented by a negative test administered on day seven or 10 -- as first reported by The Wall Street Journal. They are "right now reviewing the evidence," he said.

Demand for testing ahead of the holiday continues to strain the diagnostics system, prompting recurrent warnings from major labs that turnaround times may be delayed. Testing could become even further strapped if a shortened quarantine would require a negative test. 

When asked if the system has the ability to handle such widespread asymptomatic screening, Giroir said he was "certainly cognizant" of the turnaround times and was doing "everything possible to increase those supplies."

"Asymptomatic testing is very important, but we need to do that on targeted populations," he said. "We're not at the point that sort of every American can test themselves every day, without a reason to do that. We are trying to build that infrastructure."

ABC News' Sasha Pezenik contributed to this report

California is "in the midst of a surge," as the COVID-19 test positivity rate has increased 51% in two weeks, state Health Secretary Dr. Mark Ghaly said.

"These numbers are really going up and going up quickly," Ghaly said during a press briefing Tuesday.

The state reported 15,329 new COVID-19 cases on Tuesday. The 14-day positivity rate is 5.6%.

COVID-19 hospitalizations have gone up 81.3% over the last 14 days, and intensive care unit hospitalizations increased 57.1% during that period. There are currently 5,844 hospitalizations and 1,397 ICU hospitalizations in the state.

Ghaly warned that 12% of today's cases end up hospitalized about two to three weeks later, and that ICU units in parts of the state are already being pressed.

Four more counties also moved to California's most restrictive reopening tier on Tuesday, bringing the total number of "purple" counties to 45 -- nearly 95% of the state's population. No counties are left in the yellow tier, the least restrictive of the four.

ABC News' Bonnie Mclean contributed to this report

COVID-19 fatality rates continue to increase globally, with more than 67,000 new deaths reported in the week ending Nov. 22, according to the World Health Organization.

That continues an upward trend since mid-October, according to the WHO's weekly global epidemiological situation report.

The European region is the largest global contributor of new cases and fatalities, with Italy reporting the highest number of new cases in the region and the third-highest globally. Cases have decreased 6% in Europe, "a sign that the re-introduction of stricter public health and social measures ... is beginning to slow transmission," the report said.

The U.S. reported a 14% increase in cases and a 23% increase in deaths, according to the report. Fatalities nearly doubled over previous weeks in Puerto Rico.

The African region reported the highest increase in new cases (15%) and deaths (30%) this week, according to the report.

ABC News' Christine Theodorou contributed to this report

The actual number of people infected with the novel coronavirus in the United States reached nearly 53 million at the end of September, according to a model developed by scientists at the Centers for Disease Control and Prevention.

The scientists estimated the cumulative incidence of COVID-19 in the U.S. population by taking the laboratory-confirmed case counts that were reported nationally and adjusting them for sources of under-detection based on testing practices in inpatient and outpatient settings. Preliminary estimates using the model found that 2.4 million hospitalizations, 44.8 million symptomatic illnesses and 52.9 million total infections may have occurred through Sept. 30.

"This indicates that approximately 84% of the U.S. population has not yet been infected and thus most of the country remains at risk, despite already high rates of hospitalization," the scientists wrote in a report published in the Nov. 25 issue of the journal Clinical Infectious Diseases.

There were 6.9 million laboratory-confirmed cases of of domestically-acquired infections that were detected and reported nationally through Sept. 30. Since then, the CDC's tally has increased to nearly 12.5 million. Based on the model's ratio, the true estimated total would now be more than 95 million.