A new virus
Sandwiches caused virus outbreak
Contaminated sandwiches spread a virus which affected staff at three Jersey schools and the production company behind the Jersey Live festival.
A Health Protection Department report said the norovirus, which caused vomiting and diarrhoea, was carried in sandwiches supplied by Empire Catering.
The Health Protection Department said the firm had complied with all hygiene regulations.
It could not say how the virus ended up in the food last September.
The highly contagious norovirus affected staff at Hautlieu school and hit staff at both Haute Vallee and Springfield schools so badly they were forced to close last September.
In a report, the Health Protection Department said the link between all cases of the illness was sandwich lunches provided by Empire Catering and delivered to events held on 3 September.
Empire Catering's managing director Mario Pirrozolo said: "The ensuing Health Protection investigation confirmed that our premises were entirely compliant and there was no evidence of negligence on our part.
"We were pleased the audit revealed that there were some very good procedures in place."
The report said the virus was "food borne", but could not identify which specific sandwich or filling material was the source of the original contamination.
Steve Smith from Health Protection said: "Exactly how the infection got into the foodstuffs clearly is something we've not been able to absolutely pinpoint.
"This would have been introduced into the workplace by some form of environmental contamination."