The father of a boy admitted to Sutherland Hospital after an outbreak of food poisoning linked to a bakery in Sydney's south said victims and their families were "very angry".

NSW Health said 40 people had presented at St George and Sutherland hospitals since Saturday with symptoms of food poisoning, while 13 of those people were admitted to hospital for treatment.

But Engadine building contractor Damian Sullivan disputed these figures, saying hospital staff had told him the number of people struck down was close to 100, rather than 40.

Mr Sullivan said his son Cooper, 11, ate a chicken and salad roll from Box Village Bakery and Cafe in Sylvania for lunch on Sunday.