An outbreak of a mysterious flu-like illness in a remote part of the Democratic Republic of the Congo is a “major public-health concern” for the country that is reporting more cases, the head of the African Union’s public-health agency said. 

Congo, which is as big as the US states of Alaska and Texas combined, reported another 147 cases of “Disease X” in the past week, Africa Centres for Disease Control and Prevention Director General Jean Kaseya said in an online briefing Thursday. 

More than 500 cases of the unidentified illness have been reported since late October, with the national authorities alerted to the outbreak on Dec. 1. Most cases are among children younger than five and emerged at a time of increased influenza circulation. Dozens have died. 

Confirming the pathogen has proven difficult given how remote the epicenter of the outbreak is. The Panzi health zone in southwest Congo has no laboratories that can adequately test and diagnose the samples. This means they have to go to the capital, Kinshasa, which can take two to three days by road, compromising the quality of samples. Efforts are underway to use an airplane to transport samples for at least part the journey.

The Africa CDC expects new samples to reach Kinshasa by next week, Kaseya said. –BLOOMBERG