Authorities in Texas are keeping a close eye on five children in North Texas who came into contact with the patient, a Liberian man whom the Associated Press and Liberian health officials identified as Thomas Eric Duncan, a former shipping company employee from the Liberian capital of Monrovia.

Health officials said Wednesday that they believed the patient had contact with as many as 18 people after he fell ill, four days after landing in Dallas on a commercial flight from Monrovia, via Brussels. None has yet tested positive for Ebola. The emergency personnel who took Mr. Duncan to hospital are also being monitored, as are his Texas relatives.

Texas Health Presbyterian Hospital missed a crucial opportunity to isolate the patient earlier. The hospital sent him home with antibiotics on Friday after his travel history was "not fully communicated," to other professionals, according to an official with the hospital group that runs Texas Health Presbyterian.

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What is Canada doing to prevent Ebola-infected patients from entering this country at airports and other border crossings?

There are no direct flights to Canada from the countries hardest hit by the epidemic. Nonetheless, Canada's chief public health officer says Ebola screening has been stepped up at airports and on planes, with border guards and airline staff being instructed to watch out for sick passengers from West Africa. For instance, if airline staff spot a passenger with Ebola symptoms and a history of travel to the affected areas, the airline is supposed to alert a quarantine officer – usually a nurse – to board the plane to examine the suspected patient before he or she disembarks.

The Canada Border Services Agency has programmed an automatic reminder to pop up on all its officers' computer screens to ask travellers from Ebola-affected countries whether they are sick. "That's new," Gregory Taylor, the chief public health officer, said. "That's very specific in terms of trying to detect anybody coming from the area who could possibly be ill at the time."

Still, airport screening will not do much good if an Ebola-infected patient lands here before symptoms start. Ebola has an incubation period of two to 21 days, meaning a person can harbour the virus without appearing sick or being contagious for as long as three weeks. The U.S. patient appeared healthy when he landed in Dallas on Sept. 20. His symptoms emerged four days later.

"Screening people when they come into the airport doesn't make sense," said Michael Gardam, director of infection prevention and control at Toronto's University Health Network. "The fact remains that there is the possibility people could easily get into Canada who then subsequently develop Ebola."

How are Canadian hospitals and laboratories preparing for Ebola?

As it became clear that the Ebola outbreak in West Africa was spiralling out of control, the Public Health Agency of Canada and public health authorities at the provincial level began refreshing and updating their protocols for dealing with the virus. The goal? Identifying potential patients at hospital triage by asking them about their travel history and symptoms, then immediately isolating anyone who fits the Ebola bill.

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Dr. Taylor said that about 20 suspected Ebola cases have emerged in Canada so far. All tested negative. "This is good," he said. "This is a high index of suspicion. People are thinking about this." Right now, the bulk of Ebola testing is done on blood samples at the National Microbiology Lab in Winnipeg. But preliminary testing will soon be available at provincial labs in British Columbia, Alberta, Ontario and Nova Scotia. Quebec is already capable of performing the tests, which can swiftly rule out Ebola. Preliminary positive results would be sent to Winnipeg for confirmation, Dr. Taylor said.

Canada has already designated one hospital, Toronto Western, as the facility where Canadian aid workers would be treated if infected in West Africa. The hospital boasts expertise in tropical diseases and a special intensive-care unit constructed after the SARS crisis that includes a negative pressure suite.

However, that level of isolation is not necessary for suspected Ebola patients, according to Brian Schwartz, the chief of emergency preparedness at Public Health Ontario. "The level of isolation for something like Ebola would be contact and droplet isolation and would not require what we call a negative pressure room or an airborne infection isolation room like we [use] for tuberculosis ... a disease that's transmitted through the air, which Ebola is not."

Ebola is spread through direct contact with bodily fluids such as blood, vomit, diarrhea, saliva and semen. Dr. Schwartz said most hospitals have the means to adequately isolate suspected Ebola patients – all they need are single rooms with attached private bathrooms and an anteroom where health-care workers can safely change in and out of personal protective equipment.

How would Canada's experimental vaccine be used if a case were diagnosed here?

Canada has already shipped a "small amount" of its experimental vaccine to a hospital in Geneva and to Emory University Hospital in Atlanta, the facility that treated the first two U.S. aid workers diagnosed with Ebola in West Africa. "We're looking at doing the same in Canada, just in case," Dr. Taylor said. Dr. Taylor said the Public Health Agency of Canada is looking at shipping some of the vaccine to the "designated hospital" in Ontario, which, although he did not mention it by name, is Toronto Western.

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Dr. Gardam, the director of infection prevention and control at the network that includes Toronto Western, said he is not aware of any imminent plans to receive vials of the experimental vaccine, the bulk of which remains in storage at the National Microbiology Lab in Winnipeg.

Canada announced in August that it would donate between 800 and 1,000 doses of the vaccine, known as VSV-EBOV, to the World Health Organization for use in the outbreak, but the WHO and others have decided it is best to conduct preliminary human safety trials of the vaccine before using it on a wider scale in West Africa. Trials on the Canadian vaccine are expected to begin early this month, the WHO said Wednesday after wrapping up a two-day meeting on experimental vaccines at which experts urged the United Nations' health arm to deliver the vaccines to Africa as soon as safely possible.