The World Health Organization (WHO) has said in a statement that it has revised its Ebola virus risk assessment for the Democratic Republic of Congo (DRC) from "high to "very high", and from "moderate" to "high" at a regional level".
The fresh Ebola outbreak, publicly declared on May 8 with 23 deaths so far, was first reported in a rural part of Equateur Province in the vast country's northwest but has now spread to the city of Mbandaka.
"This is a major, major game-changer in the outbreak", Dr. Peter Salama, WHO's emergency response chief, warned on Thursday after the first urban case was announced.
The announcement came from the office of the Congo's health minister late Wednesday night after it was learned that there was a single case of Ebola reported in Mbandaka, a densely populated city just under 100 miles from the site of the last reported case.
One sample proved positive for Ebola, he said.
Cases had previously only been confirmed in Bikoro, a small town whose health clinic only has "limited functionality", according to the WHO. The total includes 20 probable cases and 21 suspected ones.
The health ministry said two new deaths have been tied to the cases, including one in a suburb of Mbandaka.
Mbandaka, a city of nearly 1.2 million, is in a busy travel corridor in Congo's northwest Equateur province and is upstream from the capital, Kinshasa, a city of about 10 million. Mbandaka is an hour's plane ride from Kinshasa or a four-to-seven-day trip by river barge, according to a map issued Thursday by the United Nations.
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Peter Salama, in charge of emergency response at the World Health Organization, has said the spread to a city complicated the fight against Ebola, which depends on identifying and isolating suspected cases.
"As more evidence comes in of the separation of cases in space and time, and healthcare workers getting infected, and people attending funerals and then traveling quite big distances - it's got everything we would worry about", he told Reuters.
Tedros Adhanom Ghebreyesus called it a concerning development.
Ebola is a highly infectious and often fatal disease.
The outbreak in West Africa that started in 2014 reached epidemic proportions and was the worst ever recorded, infecting more than 28,000 and killing more than 11,000. The vaccine is thought to be effective against the Zaire strain of Ebola found in Congo. Moreover, WHO said that no restrictions have issued on global travel.
The International Federation of the Red Cross and Red Crescent Societies said the first suspected victim was a police officer who died in a health center in the village of Ikoki-Impenge, near Bikoro.
The European Commission has announced a package of urgent humanitarian aid to help contain an outbreak of Ebola in the Democratic Republic of Congo.