The World Health Organization is warning that the fight to contain an Ebola outbreak in central Africa balances on a “knife’s edge” after two of three patients who escaped quarantine were found dead.

The patients fled quarantine in the densely populated city of Mbandaka in the Democratic Republic of Congo. The third was found alive and is under observation by the WHO. Congo’s health ministry has announced there are eight new suspected cases of Ebola. Five health workers have been infected.

That brings the total to 28 confirmed Ebola cases, 21 probable ones and nine suspected. Overall, since the outbreak of the often deadly hemorrhagic fever was confirmed by the ministry on May 8, the death toll stands at 27, with three deaths confirmed as Ebola.

The agency is accelerating efforts in nine countries that neighbour DRC, to try to prevent the spread of the current outbreak beyond its borders.

"We're on the epidemiological knife's edge of this response. The next few weeks will really tell if this outbreak is going to expand to urban areas or if we're going to be able to keep it under control," Dr. Peter Salama, the WHO emergencies chief, told a recent World Heath Assembly session.

There is no specific treatment for Ebola. Symptoms include fever, vomiting, diarrhea, muscle pain and at times internal and external bleeding. The virus can be fatal in up to 90 per cent of cases, depending on the strain.

Salama said the outbreak has three or four epicentres, making containment more challenging.

"We are following three separate chains of transmission," he said. "One associated with a funeral that took place in a neighbouring town of Bikoro; one associated with a visit to a health care facility more than 80 kilometres away in the small village of Iboko and one where we're still gathering data on that's related to a church ceremony."

Tarik Jasarevic, a WHO spokesperson, told CTV News Channel Wednesday that the agency is “redoubling its efforts” to trace the movement of anyone infected or potentially infected with the deadly disease and to offer vaccination to anyone who came in contact with them. The disease spreads by contacting bodily fluids of infected people, including the dead.

Vaccinations began this week and more than 600 contacts have been identified, according to the WHO. Newly vaccinated people would have to be monitored for 21 days.

Jasarevic said it’s not surprising that sick people flee quarantine.

“It’s very unfortunate but it’s very human for people wanting to be with their family in what they could think are the last moments of their life.”

The WHO has yet to declare the outbreak an emergency after hearing from officials in the DRC. Jasarevic said the situation is “very serious. There is a high risk of further spread at a national level and high risk at the regional level” but the emergency committee felt “all elements of the response have been mobilized very quickly and robustly.”

He said there is a “window of opportunity” to get the outbreak under control, but the situation is being monitored on a daily basis and preparations are being made for the worst-case scenario.

He said it’s difficult to contain disease in big cities and that Mbandaka, a city of 1.2 million people, is right on the Congo River, an important transportation route. Health officials are undertaking “highly targeted vaccinations.” The goal is to "build rings" around confirmed Ebola cases to halt the spread, he said.

“It is a very concerning situation.”

The WHO has deployed more than 120 people and is working with partners, including UNICEF, the United Nations, the National Science Foundation and Gavi, The Vaccine Alliance, said Jasarevic.

“We started vaccination on Monday, so we are really doing our best. It’s really difficult to speculate (on) how the outbreak can evolve. Our job is to do this as fast as we can.”

With files from The Associated Press