A 5-year-old Bronx boy who had been in isolation while being tested for Ebola on Monday at Bellevue Hospital in Manhattan was diagnosed Tuesday with a respiratory infection but will remain hospitalized, officials said.

The child, who has not been identified, was fully cleared of having Ebola after testing negative in multiple laboratory screenings and is out of isolation. The lab at the New York City Department of Health and Mental Hygiene confirmed the child's fever and illness were the result of the respiratory infection.

Dr. Craig Spencer, meanwhile, who is being treated for Ebola after a medical mission in Guinea, remains in serious but stable condition in isolation. He has been at Bellevue since Thursday.

This time of year, numerous respiratory viruses -- including the flu -- are in circulation and can trigger fever and other symptoms in children, doctors say.

Medical experts were certain as early as Monday that Ebola was an unlikely diagnosis for the child, even though he had recently traveled to Guinea, West Africa. The child was moved out of isolation Tuesday, Bellevue officials said.

In Washington, President Barack Obama said the country must continue fighting Ebola at its source, and he welcomed the Centers for Disease Control's less-stringent policy on monitoring rather than quarantining health care workers returning from Ebola hot spots. The agency's guidelines were released Monday.

Also jointly announcing support for CDC protocols Tuesday were the American Heart Association, American Medical Association and American Nursing Association. They endorsed the monitoring plan, which they say helps health care agencies attract medical volunteers.

At a news conference to thank FDNY EMS workers who took Spencer to the hospital last week, Mayor Bill de Blasio said Spencer faces challenging days ahead.

"We've said for a few days that this is a tough part of the trajectory, that things will get worse before they get better, so he's got some tough days ahead," de Blasio said Tuesday.

Spencer's fiancee and two friends remain in quarantine and are still symptom-free, de Blasio said.

The nation's eyes, he added, are riveted on the city's Ebola response.

De Blasio said he received a "very gracious" phone call from Dallas Mayor Mike Rawlings, whom the mayor said offered New York City "any part of our history that would be helpful or getting our doctors talking to your doctors."

But de Blasio also criticized Dallas' handling of the crisis.

Liberian national Thomas Eric Duncan, the first person in the United States to be diagnosed with Ebola, was initially sent home from a Dallas hospital with a useless prescription for antibiotics, according to news reports.

Despite having told hospital personnel that he had recently arrived from Liberia, Duncan wasn't immediately hospitalized. Once in isolation days later, his care reportedly followed a hodgepodge of infection control rules. Duncan died earlier this month.

"What happened in Dallas was that there wasn't a clear protocol that every individual up and down the food chain understood," De Blasio said. "And that has been the difference here."

FDNY Commissioner Daniel Nigro said 911 calls in the city for suspected Ebola cases are directed to a highly specialized squad of hazardous material and tactical experts.

The EMS team transports the patient and is met at the hospital by "decontamination specialists" who help them take their gear off "so no breach occurs," Nigro said.

De Blasio said the city began, as of Monday, monitoring people who have come back from the affected West African countries but have shown no Ebola symptoms.

"We're going the extra mile and reaching out to them," de Blasio said of keeping contact with the travelers for 21 days.

Asked about Ebola-related discrimination against medical workers or African immigrants in the city, de Blasio stressed, "The message all over the city is the situation is under control. This is a very difficult disease to contract."

FDNY HAZ TAC battalion commanding officer Paul Miano said his team was doing their duty. "We're not the type that are going to tell you that we're nervous," he said. "We're going to go in, we're going to do our job and that's our mission. And when our mission is over, we move on to the next one."

EMS workers ask patients who are suspected of having Ebola whether they've traveled, where they've traveled and whether they have a fever.

"No exposed skin. Full face piece. We use HEPA filters, so we're completely encapsulated," FDNY hazmat battalion chief Ed Bergamini said of their gear. He said the suits are disposed of as hazardous waste afterward, and in the case of Spencer's transportation were cut off so first responders could avoid touching the outside.