Dec 23 (Reuters) - Healthcare workers in the United States who test positive for COVID-19 but are asymptomatic can return to work after seven days in isolation, provided they test negative, the Centers for Disease Control and Prevention said on Thursday. The new guidance cuts the quarantine time from a previously recommended 10 days, which the CDC said was in preparation for an anticipated increase in Omicron cases. Omicron now accounts for 73% of coronavirus infections in the United States, the CDC said on Monday. The CDC said the quarantine time can be cut further if there are staffing shortages due to COVID-19, adding that healthcare workers who have been fully vaccinated, including a booster, do not need to quarantine at home following high-risk exposures. However, National Nurses United called it a dangerous decision to weaken isolation guidance for employers and demanded the CDC maintain its existing guidance. "Weakening COVID-19 guidance now, in the face of what could be the most devastating COVID-19 surge yet, will only result in further transmission, illness, and death," said Triunfo-Cortez, the president of National Nurses United. White House medical adviser Anthony Fauci had said on Tuesday U.S. health authorities were considering reducing the 10-day recommended quarantine period for Americans who test positive for COVID-19. read more