Media playback is unsupported on your device Media caption Dr Tom Frieden, CDC: "At some point there was a breach in protocol"

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*

Image copyright Map

*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.

Media playback is unsupported on your device Media caption Rajini Vaidyanathan reports from Washington

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.

Image copyright Reuters Image caption Duncan was admitted to Texas Health Presbyterian Hospital in Dallas

Image copyright AP Image caption Police are guarding the home of the infected woman

Image copyright AP Image caption A barrel labelled "biohazard" stands on a lawn outside the apartment complex of the infected health worker in Dallas

Image copyright AP Image caption Staff at the Dallas hospital have been on alert for other cases after Thomas Duncan's death

Image copyright Reuters Image caption US President Barack Obama discussed the Ebola response with Health and Human Services Secretary Sylvia Burwell by phone

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.

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.

Media playback is unsupported on your device Media caption Tulip Mazumdar describes the protective measures taken by journalists covering the Ebola crisis

Ebola deaths: Confirmed, probable and suspected

Source: WHO

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.

How not to catch Ebola:

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

Why Ebola is so dangerous

How Ebola attacks

Ebola: Mapping the outbreak

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