WASHINGTON — As the COVID-19 omicron variant surges across the United States, top federal health officials are looking to add a negative test along with its five-day isolation restrictions for asymptomatic Americans who catch the coronavirus, the White House’s top medical adviser said on Sunday. Dr. Anthony Fauci said the Centers for Disease Control and Prevention is now considering including the negative test as part of its guidance. Under that Dec. 27 guidance, isolation restrictions for people infected with COVID-19 were shortened from 10 days to five days if they are no longer feeling symptoms or running a fever. After that period, they are asked to spend the following five days wearing a mask when around others. Fauci, the nation’s top infectious diseases expert, said the US has been seeing almost a “vertical increase” of new cases, now averaging 400,000 cases a day, with hospitalizations also up. “We are definitely in the middle of a very severe surge and uptick in cases,” he said. “The acceleration of cases that we’ve seen is unprecedented, gone well beyond anything we’ve seen before.” Fauci said he’s concerned that the omicron variant is overwhelming the health care system and causing a “major disruption” on other essential services. He urged Americans who have not yet gotten vaccinated and boosted to do so and to mask up indoors to protect themselves and blunt the current surge of US cases. — Agencies