Thirty-five people have now died during a cholera outbreak in northeast Nigeria, up from 21 at the start of the week, local health officials said on Sunday.

“The number of deaths reported… is 35. The total number of suspected cholera cases is now 1,283,” the Borno state health ministry said in a statement.

Most of the cases and deaths have been at the Muna Garage camp on the outskirts of the Borno state capital, Maiduguri, which houses some 20,000 people who have fled the Boko Haram conflict.

A total of 775 infections were reported at the sprawling camp, where internally displaced people (IDPs) are living in makeshift accommodation, reliant on food handouts and communal water boreholes.

Water-borne diseases are a constant threat because of a lack of adequate sanitation for the camp dwellers, especially during the current rainy season, when poor drainage causes stagnant pools to form.

State health officials announced on September 3 that 14 people had died from 186 suspected cases of cholera in Maiduguri.

Two days later, the toll jumped to 21 from 375 cases.

Nigeria’s government, domestic and international aid agencies involved in providing shelter, food, clean water and healthcare to the IDPs have been working to contain the outbreak.

But it has spread to the town of Dikwa, some 90 kilometres (55 miles) east of Maiduguri, where 438 cases were recorded.

Suspected cases were still being investigated in the garrison town of Monguno, 138 kilometres northeast of Maiduguri, said the statement.

Maiduguri has seen its population double to two million since the start of Boko Haram’s Islamist insurgency in 2009, as the violence forced people to seek safe haven from vulnerable rural communities.

Overall, at least 20,000 people have been killed and some 2.6 million displaced.

Most IDPs live in so-called host communities with distant relatives or friends. The remainder live in camps.