The National Environment Agency (NEA) on Monday downgraded the Summer Palace restaurant and the banquet kitchen of Regent Singapore to "C" following multiple cases of food poisoning involving the two food establishments last year.

A total of 43 people who ate food from the establishments on November 11 had stomach flu - or gastroenteritis - symptoms, NEA said in an advisory.

NEA will review the grades in 12 months, and will keep the premises under surveillance in the meantime.