* WHO says prevention must be stepped up
* Four regions hit, Accra the worst affected
ACCRA, March 18 (Reuters) - A cholera epidemic in Ghana has killed 60 people and infected almost 4,000 since the first cases emerged last September, with 482 new cases reported this week alone, health authorities said on Friday.
The outbreak, which started in centre of the West African country and spread to four regions, has hit the capital Accra the worst, said Joseph Amankwah of the Ghana Health Service.
"This is a major outbreak. It's a major concern," he told Reuters by telephone. "Cases are on the increase. ... We need to address the risk factors aggressively."
Ghana has seen outbreaks of the disease roughly every five years since the 1970s, Amankwah said, adding that he believed the origin of the outbreak may be contaminated water sources following flooding last year.
Cholera is a bacterial disease spread by contaminated water and food. If caught early can be easily treated by oral rehydration fluids. If not treated, it can kill in hours.
"I wouldn't say it's out of control but it's alarming so we need to step up preventive efforts," said Sally Ohene from the World Health Organisation.
The disease has been reported in the Greater Accra, Central, Eastern and Upper Eastern regions.
Reporting by Hereward Holland; Editing by Mark John and Peter Graff