The CDC, which has helped lead the international response to Ebola, advises that all medical facilities should ask patients with symptoms consistent with Ebola for their travel history.
It's possible that others were infected because of the lapse. People who have Ebola are contagious -- but only through contact with infected bodily fluids -- when they display active symptoms of the virus, such as a high fever, severe headache, diarrhea and vomiting, among others. It's not like a cold or the flu, which can be spread before symptoms show up, and it doesn't spread through the air.
Learn how Ebola spreads
That the man had recently arrived in the United States from Liberia should have been a huge red flag. That country is one of the hotspots in a large outbreak of Ebola in West Africa, with 3,458 cases and 1,830 deaths as of September 23, according to the World Health Organization. Other countries affected include Guinea, Nigeria and Sierra Leone. In total, more than 3,000 people have died in those countries from Ebola, and more than 6,500 have contracted the disease.
This summer, two American missionaries who were working in Liberia contracted the virus and were brought back to the United States, where they were treated with the experimental drug ZMapp. Another American doctor working with the same charity was also infected in Liberia and brought home for treatment. They all have since recovered from the virus and were released from care.
The CDC has ramped up a national effort to stem the spread of Ebola, and in September President Barack Obama spoke at CDC headquarters in Atlanta. He called the virus a global health and security threat, and pledged U.S. assistance to the affected countries to try to stem the tide of the disease.