Singapore was investigating on Friday a rare cluster of cholera cases after eight people contracted the illness in the eastern part of the city-state.

“Five people are still in hospital but they are all stable. Investigations are still ongoing,” said Bey Mui Leng, a spokeswoman for the Ministry of Health.

Investigations have found most visited food stalls and restaurants in a single area and food samples from the outlets have been sent for laboratory tests.

Cholera is an acute disease caused by ingestion of food and water contaminated with bacteria. Singapore last saw an outbreak in 1999.