The Yale-New Haven Hospital in the US state of Connecticut says it has admitted a patient displaying "Ebola-like symptoms".
A statement said: "We have not confirmed or ruled-out any diagnosis at this point."
President Obama has marked the anniversary of the massacre at Sandy Hook elementary school with a moment of silence at the White House.
Before pausing to remember the Connecticut school tragedy a year ago, the president and first lady Michelle Obama lit 26 votive candles set up on a table in the Map Room - one candle for each of the 20 children and six staff members who were killed.
Church bells in Newtown, Connecticut, rang 26 times as the names of each of the victims were read at the town's St Rose of Lima church, one of several houses of worship that held private services for a community still grieving the deaths.
President Barack Obama has spoken out on gun control on the anniversary of the Sandy Hook massacre, when 27 people were killed by high school gunman Adam Lanza in Connecticut.
"We haven't yet done enough to make our communities and our country safer," Obama said. "We have to do more to keep dangerous people from getting their hands on a gun so easily. We have to do more to heal troubled minds."
The president, whose address was pre-recorded, did not refer to the shooting at a Colorado high school which left one female student in critical condition.
Obama is due to observe a moment of silence at the White House today in memory of those who died at Sandy Hook.
Earlier this year the US Senate blocked new laws that would have made it harder for Americans to buy certain types of weapons.
Today is the first anniversary of the US Sandy Hook school massacre, in which 27 people died at the hands of 20-year-old Adam Lanza.
Residents of Newton, Connecticut, will mark the date quietly, without any public memorials, and have urged others to honour the victims with random acts of kindness.
The anniversary comes a day after a student shot and wounded pupils at a high school in Colorado before shooting himself dead at the scene.
The Emergency calls that first alerted police to the massacre at Sandy Hook elementary school have been made public.
Twenty children and six of their teachers were killed by a single gunman almost a year ago.
ITV News International Editor Bill Neely reports from the US
This video contains distressing audio from the emergency calls.
Gilles Rousseau, whose daughter Lauren, a substitute teacher, was killed in the Sandy Hook school shootings, supported the decision to release the 911 call recordings.
Speaking to ITV News before their release, he said: "Personally, I think it's better to have it released because then the world will know what was in the tape. They'll know that the police is not hiding anything.
"I would like to know exactly what was in the tape. The only thing that I'm hoping for is that I don't hear my daughter screaming," he added.
"That's one of the reasons the young families did want to hear their kids screaming. They were afraid they were going to recognise their particular child, and that would be heart-wretching."
In one recording released by US authorities, a teacher at Sandy Hook Elementary School tells emergency operators she has heard shooting.
"It sounds like there are gunshots in the hallway. I'm a teacher at the school," she says.
"Keep everybody calm, get everybody away from the windows," she is told. "Try to lock down the school, OK?"
In one of the recordings released, a distressed caller is heard saying: "I think there’s somebody shooting in here at Sandy Hook School."
"What makes you think that?" she is asked.
"Because somebody's got a gun. I saw a glimpse of somebody, they're running down the hallway," she replies.
"They're still running, they're still shooting."
In an emergency call from Rick Thorne, whose job title at the time was Acting Head Custodian at Sandy Hook, gunshots are heard as he pleads "it's still going on!"
"I keep hearing shooting. I keep hearing popping," he tells the operator.
Thorne also describes how he thinks the gunman entered the building: "The front glass is all shot out. It kept going on," he says.
During the call the operator is heard asking a colleague to alert state police to the "active shooter".
Towards the end of the recording, loud bangs are heard in the background. This has been edited out of the clip above.