Washington - US health authorities on Monday issued stricter guidelines for protecting health care workers against Ebola after two Texas nurses were infected while caring for a Liberian patient.
The new instructions "provide an increased margin of safety", said Centres for Disease Control and Prevention chief Tom Frieden.
Prior to working with an Ebola patient, medical personnel must be repeatedly trained in and able to demonstrate competency in putting on and taking off personal protective equipment, said Frieden.
The gear should allow no skin to be exposed and should include gloves, a waterproof gown or coveralls, a respirator, a face shield and a disposable hood.
"Goggles are no longer recommended as they may not provide complete skin coverage in comparison to a single use disposable full face shield", said a text issued by the CDC.
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A trained observer must be present to watch every step of the process of putting on and taking off the equipment, he added.
"The greatest risk in Ebola is the taking off of whatever equipment the worker has on", said Frieden, saying the process should be "supervised and, in a way, ritualised."
The new guidelines update a previous document that the CDC issued before the nurses became infected while working in the intensive care unit to care for Thomas Eric Duncan, who died on 8 October at Texas Health Presbyterian Hospital Dallas.
"The bottom line is that the guidelines didn't work for that hospital", Frieden said.
Officials have not yet identified what happened to allow nurses Nina Pham and Amber Vinson to become infected, and Frieden said it may never be known.
He added that caring for an Ebola patient in the United States can be "riskier than in Africa", because of more high-risk procedures such as intubation.
However, he said the guidelines closely resemble those followed by Doctors Without Borders (Medecins Sans Frontieres) teams that are working in West Africa, where the largest outbreak of Ebola in history has killed more than 4 500 people since the beginning of the year.
Frieden said the CDC was working closely with hospitals that were "interested and willing" to treat Ebola patients, and was considering establishing certain expert centres in addition to the four hospitals with specialized bio containment units that already exist in the United States.