Experts have moved to calm fears of a US outbreak of the deadly Ebola virus as the first victim brought from Africa is treated at a special isolation unit at one of the nation's best hospitals.
Fear that the outbreak killing more than 700 people in Africa could spread in the US has generated public anxiety.
But infectious disease experts say there is zero risk as Emory University Hospital in Atlanta, Georgia, treats critically ill missionary Dr Kent Brantly and a charity worker infected in Liberia.
The US Centres for Disease Control and Prevention has received "nasty emails" and at least 100 calls from people saying, "How dare you bring Ebola into the country!?" CDC director Dr Tom Frieden said.
"I hope that our understandable fear of the unfamiliar does not trump our compassion when ill Americans return to the US for care," he said.
Dr Brantly and Nancy Writebol, who will arrive in several days, will be treated in Emory's isolation unit for infectious diseases, created 12 years ago to handle doctors who fall ill at the CDC nearby.
It is one of about four such units in the country, equipped with everything necessary to test and treat people exposed to very dangerous viruses.
In 2005, it handled patients with Sars - severe acute respiratory syndrome -which, unlike Ebola, can spread when an infected person coughs or sneezes.
In fact, the nature of Ebola, spread by close contact with bodily fluids and blood, means any modern hospital using standard, rigorous, infection-control measures should be able to handle it.
Nevertheless Emory will not be taking any chances.
"Nothing comes out of this unit until it is non-infectious," said Dr Bruce Ribner, who will be treating the patients. "The bottom line is: we have an inordinate amount of safety associated with the care of this patient. And we do not believe that any health care worker, any other patient or any visitor to our facility is in any way at risk of acquiring this infection."
Dr Brantly was flown from Africa to Dobbins Air Reserve base outside Atlanta in a small plane equipped to contain infectious diseases and a small police escort followed his ambulance to the hospital.
He climbed out dressed head to toe in white protective clothing, and another person in an identical hazardous materials suit held both of his gloved hands as they walked gingerly inside.
"It was a relief to welcome Kent home today. I spoke with him, and he is glad to be back in the US," said his wife Amber, who left Africa with their two young children for a wedding in the US days before the doctor fell ill.
"I am thankful to God for his safe transport and for giving him the strength to walk into the hospital."
Inside the unit, patients are sealed off from anyone who does not wear protective gear.
"Negative air pressure" means air flows in, but cannot escape until filters scrub any germs from patients. All laboratory testing is conducted within the unit and workers are highly trained in infection control.
Glass walls enable staff outside to safely observe patients and there is a vestibule where workers suit up before entering. Any gear is disposed of safely or decontaminated.
Family members will be kept outside for now.
The unit "has a plate glass window and communication system, so they'll be as close as 1-2 inches from each other," Dr Ribner said.
Dr Jay Varkey, an infectious disease specialist who will be treating Dr Brantly and Ms Writebol, gave no word about their condition. Both were described as critically ill after treating Ebola patients at a missionary hospital in Liberia, one of four West African countries hit by the largest outbreak of the virus in history.
There is no proven cure for the virus, which kills an estimated 60-80% of the people it infects, but American doctors in Africa say the mortality rate would be much lower in a functioning health care system.
The virus causes haemorrhagic fever, headaches and weakness that can escalate to vomiting, diarrhoea and kidney and liver problems. Some patients bleed internally and externally.
There are experimental treatments, but Dr Brantly had only enough for one person and insisted that his colleague receive it. His best hope in Africa was the transfusion of blood he received including antibodies from one of his patients, a 14-year-old boy who survived thanks to the doctor.
There was also only room on the plane for one patient at a time. Ms Writebol will follow in several days.