Claire Salter, a medical specialist in public health at the National Public Health Service, said Health NZ was working closely with the Ministry for Primary Industries (MPI) to investigate the cause of the outbreak.
After “epidemiological, laboratory and ecological investigations”, it was determined that the cause of the widespread disease was contamination of chicken dishes due to “improper food preparation processes”.
“Laboratory testing of stool samples provided by some of the sick students identified Clostridium perfringens.”
Clostridium perfringens is a type of bacteria that makes people sick by producing toxins.
Illness usually follows eating food that has been held at unsafe temperatures for too long, Salter said.
Food Safety New Zealand’s deputy director-general, Vincent Arbuckle, said unsafe handling practices around cooling, reheating and keeping meat warm were “consistent with how toxins from bacteria grow and cause illness”..
The amount of time between eating the food and the onset of symptoms averaged about 11 hours, which Arbuckle said is typical for the pathogen.
“If the problem is undercooked meat, we would expect to see a different pathogen, different disease symptoms and a different incubation period, usually about two to five days.”
Arbuckle said students can rest assured that food safety officials have “completely inspected the kitchen and found no evidence of an immediate and ongoing risk to food safety in the hall.”
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“Had we thought students were at risk, we would have taken further action to prevent this. Our work to review kitchen practices and procedures to prevent the problem from reoccurring continues.”
Chicken was eaten in the souvlaki meal both in the University Hall and in the Ilam Student Accommodation.
“Student responses to the survey showed that eating shredded chicken was the biggest predictor of illness,” Salter said.
The reported symptoms match the profile of the disease caused by Clostridium perfringens.
Salter said it was important to ensure the risk was properly managed to prevent it from happening again and that food safety officers had “fully inspected the kitchen and corrective action was taken”.
A student who wanted to remain anonymous told the story Things earlier that there were queues in the toilets of one building at 4am on the morning of the outbreak.
“More than 200 students were awake at all hours of the night either vomiting or suffering from extreme diarrhea,” they said.
A video posted by a student shows vomit falling from a hallway window, allegedly because the students couldn’t get to the bathroom fast enough.
NZFS food safety officers were on site the day after the initial outbreak, and the university said students unable to sit their exams due to illness would be able to apply for special consideration or resit them.