By Oct. 5, the United Nations said more than 5,000 cases of cholera had been recorded in Borno, including 178 deaths. Around half of the cases were in areas with high concentrations of people displaced by conflict.
The rapid spread appears to be linked to months of unusually heavy rains that have caused floods there and across Nigeria.
Cholera outbreaks are not uncommon in Borno, the epicenter of an ongoing Islamist insurgency that has displaced thousands into camp, straining sanitation facilities and potable water sources for well over a decade.
Large puddles of stagnant water in Maiduguri, a city of around 800,000 inhabitants, accelerated the bacteria's spread and made it difficult to contain, aid workers said.
"Compared to other years, this has been the biggest outbreak," said nurse Augusta Chinenye Obodoefuna, manager of the treatment center run by Medecins Sans Frontieres (MSF). She said patients were coming in twice as fast this year as during last year's outbreak and most of them were children.
An estimated one million people are at risk of catching the intestinal illness, which causes severe diarrhea and vomiting. Commonly spread via contaminated water and foods, it leads to dehydration and death if untreated.