A team from Doctors Without Borders dons protective clothing and equipment as they prepare to treat Ebola patients in an isolation ward of Mbandaka hospital in Congo. (Louise Annaud/Doctors Without Borders/AP)

Health officials in Congo are anxious to contain the country's deadly Ebola outbreak — which has already spread to an urban area — before the situation gets any worse. But controlling the virus may have just gotten tougher.

On Thursday, a senior Doctors Without Borders aid worker said that two patients infected with Ebola who fled their hospital on Monday night potentially exposed dozens of more people to the virus.

In a briefing in Geneva, Jean-Clement Cabrol, a doctor who had just returned from Congo, said "the patients were in the active phase of the disease, vomiting" when their families removed them from the hospital, put them on motorcycles, and took them to a religious gathering of 50 people. Ebola is contagious through bodily fluids, and both patients, who were at an acute phase of the illness, died within hours.

Those two were among the three Ebola patients who left a hospital isolation ward and reentered the general population, according to the Doctors Without Borders mission in the Congolese city of Mbandaka.

One patient left Sunday, shortly before being discharged, and is still alive, according to the aid group. The two others who attended the prayer gathering left overnight Monday; one died outside of quarantine, and another was brought back to the hospital and died there.

“In all three cases, every effort was made by staff at the hospital to convince the patients — and their families — not to leave and to continue their treatment,” Brienne Prusak, a press officer for MSF, as Doctors Without Borders is frequently known, said in a statement.

“It is unfortunate but not unexpected,” said WHO spokesman Tarik Jasarevic. “It is normal for people to want the loved ones to be at home during what could be the last moments of life.”

Now comes the challenge of determining who the patients may have come into contact with once they left the hospital in the city of more than 1 million people. There have been 58 confirmed, probable  and suspected cases of Ebola — and 27 deaths — as of Tuesday. That number could dramatically increase if the disease were to spread widely in a major city.

Knowing who has been exposed to Ebola is also critical to the effectiveness of the new Ebola vaccine that has been deployed to Congo. Proper use of the vaccine relies on identifying every person who may have come into contact with an infected individual, then working outward from there in what experts call “rings” of people, which includes contacts of contacts.

The idea is to quickly immunize those at highest risk of contracting the virus before they could potentially become infected and spread it themselves. As of this week, the WHO said 628 such contacts had been listed in Congo.

When Ebola hit West Africa in 2014, some of the obstacles that impeded the medical response included lack of trust among communities dealing with outbreaks and religious practices — such as washing the body of the dead — that spread the disease, which is contagious through bodily fluids. Community outreach to religious leaders in particular helped familiarize communities with the proper safety protocols.

But lack of trust between patients and doctors is often the reason those sick with Ebola would attempt to evade treatment, which can be intimidating when it involves isolating them from their families and only interacting with medical professionals dressed in hazmat suits. In previous Ebola outbreaks, patients have also left the hospital despite doctors urging them not to.

MSF is warning against seeing “forced hospitalization” as the solution to the outbreak.

“Patient adherence is paramount,” Prusak said. “The quicker patients are admitted, the greater their chance of survival and the greater the chance of limiting the spread of Ebola.”

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