The issue of food poisoning has been addressed by UN agencies who have imposed restrictions on melamine content in food and stricter guidelines for packaged salads.
Packaged salads could become contaminated through the water used to irrigate them, said World Health Organisation's food safety department official Jorgen Schlundt.
"In relation to salads, the issue is often that you can have contamination because you have contaminated water that you put on the fields. This can be contaminated by anything -- from human faeces to animal faeces," he said.
The new guidelines include details on the quality of water to be used on the fields as well as procedures on harvesting the salads, he said.
"The issue is to make sure that the farms are doing the right thing," he added.
There is no data for the number of people who fall sick from consuming contaminated packaged salads every year but Schlundt said there were cases in developed as well as developing countries.
He emphasised the problem of food contamination in general, saying that "at least one-third of the global population get sick from food every year."
The WHO, Food and Agriculture Organisation and the UN food standards body Codex Alimentarius Commission also set limits of the natural occurrence of melamine in food products, Schlundt said.
For powder infant milk formula the new international limit is one miligram of melamine per kilogram of formula, while for other food it is 2.5 miligrams.
The WHO stressed that melamine content in food should be its "resulting from non-intentional" presence with any intentional addition of the substance prohibited.
The tightened limit follows a scandal in China in 2008 when melamine was found to have been added to a range of products including baby formula, leading to the death of six infants with almost 300,000 falling ill.