A police car is parked Oct. 4 in front of the Ivy Apartment complex where the confirmed Ebola virus patient was staying in Dallas, Tex. (Joe Raedle/Getty Images)

The condition of Texas Ebola patient Thomas Eric Duncan deteriorated Saturday, and health officials said they are watching 49 people in the Dallas area who may have had contact with him for symptoms of the deadly disease.

Scores of other people across the country, including three in the Washington area, have been evaluated for Ebola, but none has been diagnosed with the illness.

“We have already gotten well over 100 inquiries of possible patients,” Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, said Saturday. “We’ve assessed every one of those with state and local health departments . . . and just . . . one patient has tested positive.”

The group being monitored in Texas includes nine people who almost certainly came in contact with Duncan — four in the apartment where he was staying — and about 40 others, Frieden said.

Because most people begin to show signs of infection within eight to 10 days, and Duncan became contagious Sept. 24, the next few days are a critical period in determining whether anyone else has contracted the disease from Duncan, Frieden said.

Ebola’s catastrophic effect on the body

But he noted that the incubation period can extend to 21 days.

In the Washington area, three hospital patients who were being evaluated for Ebola have been found not to have the disease.

A patient at Howard University Hospital has been “ruled out” as an Ebola case, officials there said Saturday. And a patient at George Washington University Hospital was determined to have the flu.

A third patient, who was evaluated at Shady Grove Adventist Hospital in Rockville, Md., had malaria and not Ebola, the hospital said Friday.

“Ebola has very clear symptoms that inevitably worsen over time . . . fever, bleeding from the eyes and a growing rash that consumes over 75 percent of the human body,” Joxel Garcia, director of the D.C. Department of Health, said in a statement Saturday.

The local patients were checked for the disease out of caution, officials said.

Howard hospital spokeswoman Kerry-Ann Hamilton did not specify what other illness her hospital’s patient had.

Saturday afternoon, the CDC investigated a passenger on a flight that had landed at Newark Airport.

The passenger, who according to reports in New York media was believed to be from Liberia, had vomited during the flight, said a spokeswoman for the Port Authority of New York and New Jersey, which oversees the airport.

Vomiting can be a symptom of Ebola infection, but also of other diseases common to West Africa, such as malaria.

The spokeswoman, Erica Dumas, said CDC and Port Authority workers met United Flight 998 from Brussels, which landed at 12:15 p.m., and removed a man and his daughter. The man and his daughter were taken to University Hospital in Newark.

University Hospital said in a statement on its Facebook page Saturday evening that “the symptoms of one individual were found to be consistent with another, minor treatable condition unrelated to Ebola.” The daughter was asymptomatic, the hospital said. Both were to be released but will be monitored, the statement said.

In Dallas, Duncan’s condition was downgraded from serious to critical Saturday afternoon, according to Texas Health Presbyterian Hospital there. He is isolated and in intensive care.

The 49 people who will be monitored for 21 days in Dallas include some who later rode in the ambulance that took Duncan to the hospital Sept. 28, when he became violently ill with Ebola.

Frieden said officials couldn’t be entirely sure that they did not come in contact with the virus and will track their conditions.

The nine highest-risk people include an unspecified number of health-care workers who came in contact with Duncan while he had symptoms of the lethal hemorrhagic disease but before he was isolated at the hospital.

Another four were living in the Dallas apartment where the Liberian man was staying. They have been moved to a private home that was donated anonymously.

Elsewhere, there have been numerous false alarms.

“We expect that we will see more rumors, or concerns or possibilities of cases,” Frieden said Saturday. “Until there is a positive laboratory test, that is what they are: rumors and concerns.”

Frieden said that officials want to hear of possible cases — but cases of people who have symptoms and who have traveled to Guinea, Sierra Leone or Liberia in the past 21 days.

The outbreak in Nigeria may be over, he said.

“We think transmission there . . . has ended,” he said.

Overall, the deadliest Ebola outbreak in history has killed at least 3,439 people in West Africa and infected thousands more, according to the World Health Organization.

But before the Dallas case was confirmed this past week, there had not been a single Ebola diagnosis in the United States.

Potential Ebola patients who were evaluated in New York, California, New Mexico and Miami all tested negative for the virus.

People with Ebola are not contagious until they begin showing symptoms, which include a fever of greater than 101.5 degrees Fahrenheit, severe headache and vomiting. And you can get Ebola only through contact with a contagious person’s bodily fluids.

Several Ebola patients have been transported from West Africa to the United States, including three Americans who were in Liberia — doctors Richard Sacra and Kent Brantly and missionary worker Nancy Writebol — who have already been discharged after they were successfully treated here. A Liberian American, Patrick Sawyer, fell ill after traveling to Nigeria and died of the disease.

Sacra was admitted to UMass Memorial Medical Center in Worcester, Mass., on Saturday with a respiratory illness, according to a report by WCVB (Channel 5) in Boston. Doctors said it was unlikely that Sacra has suffered an Ebola relapse.

“Because of his recent battle with the Ebola virus, his immune system is compromised,” said Phil Smith, the doctor who initially treated Sacra for Ebola at the Nebraska Medical Center. “The symptoms he has are indicative of a respiratory illness and are not those of someone suffering from Ebola.”

The NIH in Bethesda recently admitted an American patient who had been exposed to Ebola.

On Thursday night, NBC News announced that a freelance cameraman working for the network in Liberia has tested positive for Ebola and will return to the United States for treatment.

Elahe Izadi, Susan Svrluga and Abby Ohlheiser contributed to this report.