Howard University Hospital in Washington, D.C. (Sarah L. Voisin/The Washington Post)

UPDATE: The District of Columbia Department of Health and the U.S. Centers for Disease Control and Prevention said on Saturday that they have ruled out Ebola for the patient at Howard University Hospital.

EARLIER STORY: Two Washington area hospitals said within hours of each other Friday that they had each admitted a patient with symptoms and travel histories associated with Ebola.

A person who had recently traveled to Nigeria came to Howard University Hospital in the District overnight "presenting symptoms that could be associated with Ebola," spokeswoman Kerry-Ann Hamilton said in a statement.

"In an abundance of caution, we have activated the appropriate infection control protocols, including isolating the patient," she said. "Our medical team continues to evaluate and monitor progress in close collaboration with the CDC and the Department of Health."

Just hours later, Shady Grove Adventist Hospital in Rockville, Md., north of Washington, confirmed that it was evaluating a patient who "presented with flu-like symptoms and a travel history that matches criteria for possible Ebola."

But on Friday night, Shady Grove Adventist officials said they had ruled out Ebola. "Our medical team has determined that the patient has malaria and does not have Ebola," the hospital said in a statement.

While Ebola continues to devastate West African nations including Liberia and Sierra Leone, the outbreak in Nigeria – where the Howard patient had traveled – may actually be coming to an end, with no new cases since Aug. 31, the CDC reported earlier this week. At one point, 894 people in Nigeria were being monitored since they had come into contact with someone sick with Ebola.

Here's how the virus spreads and how contact tracing works to stop outbreaks. (Gillian Brockell/The Washington Post)

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 an Ebola case was confirmed in Dallas this 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.

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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 only get Ebola 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.

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.

In Maryland, all health providers and labs are required to report suspected Ebola cases to the state Department of Health and Mental Hygiene immediately, said spokesman Christopher Garrett. The state agency works with local health departments to ensure that proper procedures, including isolation, are followed; information has been distributed to hospitals, nursing homes, labs and other providers.

Officials at several local hospitals said they have been following CDC guidelines. At the University of Virginia Health System, an emerging-infectious-diseases work group was formed earlier this year to respond to MERS; this summer, that group began preparedness planning for the possibility of Ebola infections.

The system has already been tested; the University of Virginia Health System has had one patient who met CDC criteria for Ebola screening, based on travel history, fever and other symptoms.

"We confirmed that concern with public health authorities and went through the formal process of admitting and evaluating that person for Ebola,” said Costi Sifri, director of hospital epidemiology, infection prevention and control. “We ruled out the possibility of Ebola.”

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[This post has been updated.]