Cholera has killed 15 people and made 547 sick in Zambia’s capital Lusaka.
The rising caseload is expected to grow further as the rainy season starts, according to the World Health Organization.
The outbreak began in September but the number of cases surged, with 136 about two weeks ago.
The main affected areas are the densely populated districts of Lusaka, Chipata and Kanyama, where poor sanitation may favour the spread of the disease.
“The coming of the rainy season, coupled with inadequate water supply and sanitation, increases the risk of outbreaks in Lusaka and other parts of the country,” WHO said.
There is also a high risk of disease outbreaks in Zambia’s Nchelenge refugee camp, which is more than 1,000 km from Lusaka.
The camp holds more than 60,000 refugees, mainly from Democratic Republic of Congo, which is also suffering a cholera outbreak.