(CNN) -- Thomas Eric Duncan left Africa for the United States, by official accounts, a healthy man.
But within days after his arrival in Texas, things changed for him, for the worst.
So who is Duncan, besides the first person to be diagnosed with Ebola in the United States? When did he start to feel sick, and what happened to him next? And who did he come in contact with, in the meantime?
Who is Thomas Eric Duncan?
He is a 42-year-old Liberian citizen, said a friend who knows him well but asked not to be identified because of the sensitivity of his case.
Duncan's Facebook page indicates that he's from the Liberian capital of Monrovia, where he attended E. Jonathan Goodridge High School.
Why did he come to the United States?
To visit family and friends, according to the friend, who noted this was Duncan's first trip to America. Centers for Disease Control and Prevention director Thomas Frieden has said that Duncan was "staying with family members who live in this country."
Stanley Gaye, a Liberian community leader in Dallas, said Duncan was in Dallas visiting his girlfriend.
When did Duncan leave Liberia?
He departed the West African nation on September 19, Frieden says.
How did he get Ebola?
Authorities haven't said.
The New York Times reported Thursday that Duncan had direct contact with a pregnant woman stricken with Ebola on September 15, days before he left for the United States. Citing the woman's parents and Duncan's neighbors in Monrovia, Liberia, the newspaper said Duncan had helped carry the ailing woman home after a hospital turned her away because there wasn't enough space in its Ebola treatment ward.
A CDC spokesman told CNN on Wednesday that he hadn't seen the newspaper's report and couldn't comment.
Was he screened for Ebola before getting on the plane?
Yes, according to Jay Nagbe Sloh, the director-general of the state-run Liberia News Agency.
Duncan was tested "like all other passengers" at Roberts International Airport, located about 60 kilometers (35 miles) east of the capital Monrovia, said Sloh. "He showed no Ebola signs" -- such as high fever, sweating, vomiting or weakness -- "when tested."
So where did he go next?
Sloh, from the Liberia News Agency, said that Duncan boarded an SN Brussels Airlines flight. That plane took him first to the Belgian capital, and he then flew to the United States, where he arrived September 20.
He was on two United Airlines flights -- Flight 951 from Brussels to Washington Dulles and Flight 822 from Washington Dulles to Dallas-Fort Worth -- during that trip, according to a spokesperson for the airline who did not want to be named.
When did his Ebola symptoms appear?
"Four or five days" after his trip, according to the CDC's Frieden.
This doesn't mean that Duncan actually got infected with Ebola in the United States. The incubation period for the virus is 2 to 21 days, meaning that a person could be infected with the disease for up to three weeks before he or she show any signs of it.
When he did seek medical help?
After 10 p.m. Thursday, September 25. That's when Duncan first walked into Texas Health Presbyterian Hospital Dallas, according to a statement Wednesday. (A hospital official had earlier said that he'd gone to the hospital Friday.)
His friend said that Duncan had a fever and vomiting during this first visit to the Dallas hospital. The hospital, in a statement Wednesday, said he had a "low grade fever and abdominal pain."
He underwent basic blood tests, but wasn't screened for Ebola, said Dr. Edward Goodman from the Dallas hospital. Duncan left the medical facility after being given antibiotics and a pain reliever, his friend said.
"His condition did not warrant admission," the hospital said. "He also was not exhibiting symptoms specific to Ebola."
Were flags raised that Duncan might have Ebola?
After being asked by a nurse, Duncan did say that he'd traveled from Africa, said Dr. Mark Lester, executive vice president of Texas Health Presbyterian's parent company.
But that detail -- which might have raised an alarm that Duncan might have Ebola, since Liberia is one of the countries hardest hit by the virus -- was not "fully communicated" to the medical team, according to Lester.
When was he admitted to Texas Health Presbyterian Hospital?
The friend -- frustrated and feeling hospital staff wasn't doing enough -- then reportedly called the CDC about Duncan's case. The CDC told the friend to call Texas' Department of Health, with the message eventually getting to the hospital.
This description, however, runs counter to what Texas Health Presbyterian said in its statement Wednesday. By the time Duncan arrived via ambulance, "EMS had already identified potential need for isolation," the hospital said. "The hospital followed all suggested CDC protocols at that time."
Who did the patient come into contact with in the meantime?
Given the timetable outlined by Frieden, that leaves a few days between when Duncan began to show signs of Ebola and when he was hospitalized. This is significant because someone with Ebola is only contagious when they are symptomatic. And, obviously, there are more safeguards to prevent infection in a medical environment than outside of it.
Officials say they have identified 12 to 18 people who Duncan came into contact with in the United States since he became contagious.
That number includes five students who attended four different schools in the area, according to Dallas Superintendent Mike Miles.
They are Duncan's girlfriend's children, according to Gaye, the Liberian community leader.
Those children are being monitored at home, though none have exhibited Ebola symptoms.
"They are doing well. ... They are doing fine," he said. "All she asks for are our prayers."
It's not known yet whether they or anyone else got Ebola -- which only spreads through contact with infected bodily fluids -- because of Duncan. This includes members of the ambulance crew that transported him to the hospital; none of had shown symptoms, Dallas Mayor Mike Rawlings said Tuesday.
How is Duncan doing?
"All right," according to his friend, who has spoken with Duncan frequently. "He is in pain."
The friend, who talked with Duncan as recently as Wednesday afternoon, said that Duncan hasn't eaten in a week.
Texas Health Presbyterian Hospital spokeswoman Candace White said that Duncan is in serious condition at her Dallas hospital.
CNN's Jennifer Bixler, Elwyn Lopez, Aaron Morris, Jason Morris, Danelle Garcia and Gary Tuchman contributed to this report.
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