A US health chief has said a mistake was "clearly" made by hospital staff treating an Ebola victim in Texas, resulting in one member being infected.
The US Centers for Disease Control and Prevention (CDC) has confirmed that a female health worker tested positive for the deadly virus in Dallas.
CDC chief Dr Tom Frieden has promised a full inquiry into how the transmission could have occurred.
He said 48 other people who may also have had contact were being observed.
The health worker at Texas Health Presbyterian Hospital is now on an isolation ward and is said to be in a stable condition.
She had been treating Ebola victim Thomas Eric Duncan, who caught the virus in his native Liberia and died on Wednesday.
The current Ebola outbreak, concentrated in Liberia, Guinea and Sierra Leone, has resulted in more than 8,300 confirmed and suspected cases, and at least 4,033 deaths.
In other developments
- The health authorities in Sierra Leone say they are now treating more Ebola patients in the capital Freetown than in the eastern districts of Kenema and Kailahun, where the first cases in the country were detected
- European health officials investigating how a nurse in Madrid caught Ebola told the BBC they believe it was simply the result of an accident and the risks to the wider population remain very low
- The UN special envoy on Ebola told the BBC the number of Ebola cases was currently increasing exponentially, but greater awareness would help contain the virus
Ebola patients treated outside West Africa*
*In all cases but two, first in Madrid and later in Dallas, the patient was infected with Ebola while in West Africa.
'Clearly a breach'
Dr Frieden said a full investigation would be conducted into how the infection had occurred.
"Clearly there was a breach in protocol," he told US broadcaster CBS.
The CDC investigation, he told reporters, would focus on possible breaches made during two "high-risk procedures", dialysis and respiratory intubation.
The health worker who was infected has not been able to identify a specific breach of protocol that might have led to her being infected, he said.
Dr Daniel Varga, of the Texas Health Resource, said she had worn a gown, gloves, mask and shield when providing care to Duncan during his second and final hospital admission.
Dr Frieden said education and training of health workers would be stepped up and efforts would be made to reduce the number of staff treating Ebola cases.
Police are guarding the apartment complex where the woman lives in Dallas as decontamination work is carried out.
Officials have been knocking on doors, making automated phone calls and passing out fliers to notify people within a four-street radius about the situation, while seeking to reassure local people.
No details of her identity or position at the hospital have been given, in accordance with family wishes.
Flight from Monrovia
Duncan tested positive in Dallas on 30 September, 10 days after arriving on a flight from Monrovia via Brussels.
He had become ill a few days after arriving in the US, and went to the hospital in Dallas with a high fever.
Protective Ebola suit×
The cap forms part of a protective hood covering the head and neck. It offers medical workers an added layer of protection, ensuring that they cannot touch any part of their face whilst in the treatment centre.
Goggles, or eye visors, are used to provide cover to the eyes, protecting them from splashes. The goggles are sprayed with an anti-fogging solution before being worn. On October 21, the US Centers for Disease Control and Prevention (CDC) announced stringent new guidelines for healthcare personnel who may be dealing with Ebola patients. In the new guidelines, health workers are advised to use a single use disposable full face shield as goggles may not provide complete skin coverage.
Covers the mouth to protect from sprays of blood or body fluids from patients. When wearing a respirator, the medical worker must tear this outer mask to allow the respirator through.
A respirator is worn to protect the wearer from a patient's coughs. According to guidelines from the medical charity Medecins Sans Frontieres (MSF), the respirator should be put on second, right after donning the overalls.
A surgical scrub suit, durable hospital clothing that absorbs liquid and is easily cleaned, is worn as a baselayer underneath the overalls. It is normally tucked into rubber boots to ensure no skin is exposed.
The overalls are placed on top of the scrubs. These suits are similar to hazardous material (hazmat) suits worn in toxic environments. The team member supervising the process should check that the equipment is not damaged.
A minimum two sets of gloves are required, covering the suit cuff. When putting on the gloves, care must be taken to ensure that no skin is exposed and that they are worn in such a way that any fluid on the sleeve will run off the suit and glove. Medical workers must change gloves between patients, performing thorough hand hygiene before donning a new pair. Heavy duty gloves are used whenever workers need to handle infectious waste.
A waterproof apron is placed on top of the overalls as a final layer of protective clothing.
Ebola health workers typically wear rubber boots, with the scrubs tucked into the footwear. If boots are unavailable, workers must wear closed, puncture and fluid-resistant shoes.
But despite telling medical staff he had been in Liberia, he was sent home with painkillers and antibiotics.
Duncan was later put into an isolation unit at the hospital but died despite being given an experimental drug.
Symptoms of Ebola include fever, headache, vomiting, diarrhoea and bleeding. The virus is spread through contact with bodily fluids.
Ebola deaths: Confirmed, probable and suspected
Note: figures have occasionally been revised down as suspected or probable cases are found to be unrelated to Ebola. They do not include one death in the US recorded on 8 October.
- Avoid direct contact with sick patients
- Wear goggles to protect eyes
- Clothing and clinical waste should be incinerated and any medical equipment that needs to be kept should be decontaminated
- People who recover from Ebola should abstain from sex or use condoms for three months
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