Unsafe preparation of shredded chicken is what caused students at Canterbury University to get food poisoning, New Zealand Food Safety has confirmed.
More than 150 students became unwell this month after eating a chicken souvalaki dinner provided at the Unihall and Ilam Apartments.
It resulted in queues for the toilets and some people vomiting from windows because they could not make it in time.
The University of Canterbury Students' Association has confirmed it runs UniLodge's Maidstone Road kitchen that provides catering at both halls of residence through its OnCampus division.
NZ Food Safety deputy director-general Vincent Arbuckle said the bacteria Clostridium perfringens was identified as the cause, after it was found in faecal samples from students who became ill.
"Unsafe handling practices around cooling, reheating and hot holding of the meat is consistent with how toxins from the bacteria grow and cause illness."
Arbuckle said the amount of time between the food being eaten and symptoms appearing was about 11 hours on average, which was typical of this pathogen.
He said if the issue was undercooked meat there would be a different pathogen; other symptoms of illness and a different incubation period, typically around two to five days.
"This conclusion is supported by data collected by the National Public Health Service, including faecal samples provided by some affected students, and a survey of students to establish what they ate and the symptoms they experienced."
Arbuckle had a message for businesses who cater to large numbers.
"Businesses which cater for large numbers of people, such as a university halls of residence, need to make sure that where they prepare and cook food in bulk they have good processes in place to make sure risk is properly managed.
"In particular, cooling and reheating must be carefully managed to prevent pathogens from growing, and particular care must be taken when keeping food for later service.
"Students can be assured that food safety officers have fully inspected the kitchen and found no evidence of immediate and ongoing food safety risk at the hall.
"If we thought students were at risk we would take further actions to prevent it. Our work to review the kitchen's practices and procedures to prevent the issue from arising again continues," he said.
