A health worker watches as a burial team collects Ebola victims from a Ministry of Health treatment center for cremation on October 2, 2014 in Monrovia, Liberia. Getty Images

The first Ebola patient diagnosed in the United States took a turn for the worse on Saturday, slipping from serious to critical condition, as health officials reported fielding scores of possible cases around the country that proved to be false alarms. Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, said news of the Ebola patient in Dallas had alerted hospitals nationwide to check incoming patients for potential risks, particularly those who had recently traveled from the center of the outbreak in West Africa. The CDC has identified nine people who had contact with the Dallas patient from Liberia, Thomas Eric Duncan, and therefore may have been exposed to the virus, and an additional 40 are being monitored as potential contacts. None have shown symptoms, Frieden said. Read MoreDallas hospital alters Ebola account Frieden also said U.S. health authorities have responded to inquiries regarding more than 100 potential cases of Ebola since Duncan tested positive earlier this week, but no new infections have been identified. On Saturday, CDC officials dressed in biohazard suits escorted two passengers off a United Airlines jet that landed at Newark Liberty International Airport in New Jersey because they were believed to be from Liberia and exhibiting signs of illness during the flight. Read MoreBan passengers from Ebola countries?

The CDC says a full evaluation of the man at a local hospital showed "no evidence or concern for Ebola" and he was discharged "feeling well." State health officials say the man's symptoms were consistent with a minor, treatable illness. Port Authority spokeswoman Erica Dumas says the man began throwing up during the flight. Authorities say the plane's crew and roughly 250 passengers stayed onboard while officials tended to him.



Duncan's diagnosis "has really increased attention to what health workers need to do to be alert and make sure a travel history is taken,'' Frieden told a news conference. Frieden added that many of the inquiries fielded by the CDC involved people who had traveled outside West Africa. Read MoreContagious? Measles. Ebola? Not much Duncan, now being treated at Texas Health Presbyterian Hospital, was sent home after his first visit to the emergency room, despite telling a nurse there that he had just been to Liberia. The hospital issued a terse statement on Saturday saying he was in critical condition, a worsening from the "serious condition'' he was listed in the previous two days. The hospital declined to elaborate. The governments of Guinea, Sierra Leone and Liberia are struggling to contain the worst outbreak on record of the deadly hemorrhagic fever. The World Health Organization on Friday updated its death toll to at least 3,439 out of 7,492 suspected, probable or confirmed cases.

10 people remain in isolation