The specter of the virus spreading through Nigeria is particularly alarming, said David Morse, an epidemiology professor at Columbia University's Mailman School of Public Health.
"It makes you nervous when so many people are potentially at risk," he said.
Lagos is a bewildering combination of wealth and abject poverty, awash in luxury SUVs and decrepit buses alike that carry passengers through hours of crowded traffic on the bridges linking the city's islands to the mainland.
Ebola can only be transmitted through direct contact with the bodily fluids of someone who is sick - blood, semen, saliva, urine, feces or sweat. Millions live in cramped conditions without access to flushable toilets, and signs posted across the megacity tell people not to urinate in public.
Authorities in Liberia said Sawyer's sister had recently died of Ebola, though Sawyer said he had not had close contact with her while she was ill.
In announcing his death, Health Minister Onyebuchi Chukwu maintained that Nigerian officials had been vigilant.
"It was right there (at the airport) that the problem was noticed because we have maintained our surveillance," he told reporters. "And immediately, he went into the custody of the port health services of the federal ministry of health so there was no time for him to mingle in Lagos. He has not been in touch with any other person again since we took him from the airport."
On Tuesday, the Lagos state health commissioner said, however, that they did not suspect Ebola immediately and it was only after about 24 hours in the hospital that they identified him as a possible Ebola case.
Lagos state health commissioner Jide Idris said Tuesday that the nature of his disease "was not known" the first day.
"They went back to the history and they were like `Oh, this is Liberia,' and that's why he was put into isolation," he told reporters. "So even in that window period it was possible that some of these people got infected."
Sawyer, who had a fever and was vomiting, was coming from the infected country of Liberia but had a layover in Togo. As a result, officials may not have initially known his original destination.
Experts say people infected with Ebola can spread the disease only through their bodily fluids and after they show symptoms.
Since the incubation period can last up to three weeks, some of the Nigerians who treated Sawyer are only now showing signs of illness that can mimic many common tropical illnesses - fever, muscle aches and vomiting.
The national health minister on Wednesday said special tents would be used to speed up the establishment of isolation wards in all of Nigeria's states. Authorities also were setting up an emergency center to deal with Ebola that would be "fully functional" by Thursday.
"We are embarking on recruiting additional health personnel to strengthen the team who are currently managing the situation in Lagos," said his statement.
