(Bloomberg) -- Malawi’s worst cholera outbreak in two decades has left 643 people dead after the disease spread to all districts of the southeastern African country. 

The landlocked nation, prone to tropical storms and cyclones, has been battling a resurgence of the water-borne diarrheal disease since March. The rainy season, which began in November, worsened the situation. Floods have led to the displacement of people, who often lack access to safe water and sanitation. 

With the case fatality rate climbing to 3.4%, government has delayed the opening of schools for the year in both the political capital Lilongwe and in Blantyre, the nation’s center of finance and commerce. An outbreak that started in April 2001 killed 968 people in the country, according to the World Health Organization.

While most people can be treated successfully through prompt administration of oral rehydration solution, climate change and armed conflict have added to the risk of cholera outbreaks in communities that have low pre-existing immunity. In 2022, these included Haiti, Pakistan and Nigeria.

An increase in case numbers in several countries has depleted cholera vaccine stockpiles. In October, the WHO and its partners decided to limit all reactive oral cholera vaccine campaigns to a single dose.

Malawi’s outbreak, which started in the southern region, has been controlled in four of its 29 districts, Health Minister Khumbize Kandodo Chiponda said in a statement. The country’s north, however, is now the epicenter, with 21- to 30-year-olds the most affected, according to the WHO. Cholera prevention protocols have been implemented in schools, the minister said.

The “significant increases in numbers” means that the Africa Centres for Disease Control and Prevention needs to “act swiftly to support Malawi to bring this particular cholera outbreak under control,” Ahmed Ogwell Ouma, the agency’s acting director said during a briefing Thursday. 

This is especially important because “it’s affecting the most economically active age group,” he said. Systems must be put in place so that is “never becomes this big again.”  

Haiti has reported 13,672 suspected cases of cholera, including 238 deaths, since an outbreak began Oct. 2. That brings its case fatality rate to 2.1%. 

(Updates with Africa CDC comment from seventh paragraph)

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