DALLAS (Reuters) - 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.

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, WABC-TV and the Record newspaper reported.

An airport official was quoted by the newspaper as saying CDC officials did not believe the pair, a man and his daughter, were sick with Ebola. The official added that all other passengers on the flight from Brussels were cleared to leave the plane.

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.

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.

TEN PEOPLE REMAIN IN ISOLATION

On Friday, officials said the number of people placed under isolation in Dallas after possible exposure to Duncan had grown to at least 10, including four members of a family moved to an undisclosed house for close monitoring.

Initially, 100 people had been feared to have had direct or indirect contact. All those in isolation were cooperating with public health authorities by staying in quarantine voluntarily, according to Dallas city and county officials.

“There’s no one under orders. There’s no one that we perceive that needs to be under orders,” Judge Clay Jenkins, Dallas County’s top elected official, told a news conference late on Friday.

Separately, five public school children who had possibly been exposed to the Ebola patient had been kept home from class in recent days while being monitored as a precaution, though none had shown any symptoms, said Mike Miles, superintendent of the Dallas Independent School District.

Authorities have said the individuals placed in isolation included the four members of a single family whose apartment Duncan was staying in when he fell ill after traveling to Dallas from Liberia on Sept. 19. The six others are healthcare workers, including those who transported Duncan by ambulance on his second trip to the hospital on Sept. 28.

Duncan became ill on the night of Sept. 25 and visited the emergency room at Presbyterian Hospital, but was sent home with antibiotics and not screened for Ebola, despite telling a nurse there that he had just been to Liberia.

The hospital issued a statement on Friday saying that Duncan’s travel history was “documented and available to the full care team,” including doctors, through electronic records, contrary to the hospital’s earlier assertions that staff were not made aware of his recent presence in West Africa.

Just days before flying to Texas via Brussels and Washington, Duncan had helped a pregnant woman who later died of Ebola in Liberia, a fact that he concealed from airport authorities in Liberia before boarding the plane.

Dallas County District Attorney Craig Watkins told a Dallas NBC News affiliate his office was considering whether to pursue a possible criminal case against Duncan, though he did not specify on what basis Duncan might be charged.

The woman with whom he was staying, publicly referred to by city officials by her first name only but identified in the media as Louise Troh, was later ordered to stay inside her apartment with her 13-year-old son and two adult nephews who lived there with her.

On Friday, the family agreed to move voluntarily to an isolated four-bedroom house in a gated community in an undisclosed location somewhere within city limits, Jenkins said.

Arrangements for making the home available were made through a “faith friend,” Jenkins said, describing the house as spacious and well equipped with amenities. He said the family members were free to venture outdoors on the property.

In the meantime, a cleanup crew contracted by local public health authorities finished the task of sanitizing the family’s own apartment and removing perspiration-soaked bed linen, towels and other items used by Duncan.

Jenkins said the materials were placed in plastic bags, doused with bleach and then sealed in plastic barrels that were loaded onto trucks for shipment to an undisclosed location.

The hazardous materials trucks left the Ivy Apartments complex in Dallas on Saturday morning, bringing a sense of relief to neighbors worried about the virus.

“We are happy that they are gone,” Thapa Lal Bahadur, an immigrant from Bhutan said, referring to the cleanup crews. “We had a fear about that virus.”