When someone swallows bacteria that cause food poisoning, there is a delay (incubation period) before symptoms begin. This is because most bacteria that cause food poisoning need time to multiply in the intestine. The length of the incubation period depends on the type of bacteria and how many are swallowed.It could be hours or days.almonella. Salmonella is the second most common cause of food poisoning after campylobacter. It has been found in unpasteurised milk, eggs and raw egg products, meat and poultry. It can survive if food is not cooked properly.