The two medical workers at the provincial hospital in the northern Angolan region hit by the outbreak -- the worst ever recorded -- were exposed to blood from infected patients because they were working without adequate safety procedures, the World Health Organization said.

"We can't say the virus is under control," said WHO spokesman Iain Simpson. "It is clear the virus is still circulating in the community."

Simpson said it was believed safety procedures had since been improved at the hospital.

There is no vaccine for Marburg, which spreads through contact with bodily fluids and can kill rapidly.

Angolan Health Minister Sebastiao Veloso had said Thursday he was hopeful that the Marburg outbreak could soon be brought under control after officials reported no new cases between noon Tuesday and noon Wednesday.

Veloso said the outbreak would be declared officially under control after 21 consecutive days without new infections.

The incubation period for the virus or the amount of time it takes between becoming infected and falling ill, can be 21 days. WHO does not consider outbreaks to be contained until there have been no new infections for a period lasting double the maximum incubation time.

But Simpson said such predictions were at this point still unrealistic and warned of future setbacks.

"I wouldn't say it's out of control, but I wouldn't say it's under control either," WHO's Simpson told reporters Friday. "We can't say that there won't be more new cases -- in fact, we expect there will be more cases."

"If the infection control isn't strong enough to protect the health staff, clearly there are problems," he added.

Last week WHO criticized procedures at the northern Angolan provincial hospital, noting that doctors had been exposed and that other safety protocols had been breached.

Simpson said Friday, "Those problems we think have now been addressed. We think the infection control in the hospital has now improved and we hope that we won't see any more cases among health workers."

WHO has reported 308 cases of Marburg fever in the Angolan outbreak. Of these cases, 277 were fatal.

The last and previously most severe outbreak of Marburg occurred in Congo, which neighbors Angola, between 1998 and 2000, killing 128 people.

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