(Reuters) – A man in Massachusetts who was being evaluated at a Boston hospital for a possible Ebola infection does not appear to have the deadly disease, officials at Beth Israel Deaconess Medical Center said on Sunday night.

The patient, who recently returned from Liberia, had complained of headache and muscle aches, prompting his admittance to an isolation ward with close monitoring, the hospital said.

“This patient does not appear to meet CDC criteria to be considered someone at high risk for Ebola and the likelihood of Ebola Virus Disease is extremely low,” the hospital said in a statement emailed to Reuters.

Even so, the patient will remain in isolation, the hospital said.

The response in Massachusetts demonstrates the high state of alert medical facilities are under since a Texas health worker became the first person on Sunday to contract the disease in the United States. She had treated a Liberian man who died of the deadly virus last week.

“We are taking all necessary precautions in collaboration with the city of Boston and the department of public health for the potential that this is suspected Ebola,” Dr. Kenneth Sands, chief quality officer at Beth Israel, said at a news conference. “We are only at the stage where we are doing an assessment.”

There have been several Ebola scares in the United States in the past week. A plane was briefly quarantined at a Las Vegas Airport on Friday after a passenger reported feeling unwell. Health officials around the country have fielded scores of possible cases that were false alarms.

On Sunday, a United Airlines flight from John F. Kennedy Airport in New York landed at an isolated terminal at Los Angeles International Airport after a passenger who had recently visited Africa began vomiting and running a fever, officials said.

However, it turned out that the woman had visited South Africa, which is not an area of concern for Ebola.

The Massachusetts patient first reported to the Harvard Vanguard Medical Associates hospital in Braintree, Massachusetts, and was then transferred to Beth Israel, said Ben Kruskal, a physician and chief of infectious disease at Vanguard, in a statement.

Kruskal said the Braintree building was closed briefly but reopened

The current Ebola outbreak, the worst on record of the disease, has killed more than 4,000 people, mostly in Liberia, Sierra Leone and Guinea in West Africa.

(Reporting by Kevin Murphy in Kansas City, Peter Cooney in Washington, Frank McGurty in New York and Sharon Bernstein in Sacramento; Editing by Lisa Shumaker, Eric Walsh and Michael Perry)