A patient is wheeled outside the emergency room of Maimonides Medical Center in Brooklyn, New York, the United States, on Dec. 3, 2020. (Photo by Michael Nagle/Xinhua)

It took only five days for the United States to add 1 million new COVID-19 infections, the highest growth rate since the outbreak of the pandemic. Experts are expecting the spread to worsen, anticipating new waves from December holiday gatherings on top of a potential surge from the Thanksgiving week.

WASHINGTON, Dec. 8 -- The United States has set new world records for COVID-19 core metrics including hospitalizations, seven-day average case and death increases, as the total number of confirmed cases topped 15 million on Tuesday.

It took only five days for the country to add 1 million new infections, the highest growth rate since the outbreak of the pandemic in the country.

The nation recorded over 186,000 new daily cases and 1,500 deaths on Monday, bringing the seven-day average daily case increase to a record-high of 196,500 cases, according to data updated Tuesday by the U.S. Centers for Disease Control and Prevention.

The seven-day average daily deaths stood at 2,211 as of Monday, also the highest since April 25.

The country has averaged about 2,237 daily coronavirus deaths across a week, just below its highest-ever average of 2,241 set on April 24, CNN cited Johns Hopkins University data as showing.

Cases and hospitalizations have kept soaring in the country recently, as health care staff and facilities are under extreme pressure to take care of burgeoning numbers of patients.