More than 50 students and teachers from three local secondary schools contracted gastroenteritis after dining at the same restaurants during an exchange trip to Shaoguan in Guangdong province.
However, the bureau said preliminary investigations by mainland authorities showed no proof that the infections were caused by the arranged meals during the tour.
It added that the investigations revealed that the outbreak was likely spread through daily contact between tour members or exposure to vomit.
As a precaution, the bureau said it has also ordered all restaurants serving mainland study tours to temporarily stop serving raw and cold food.
The bureau stressed that it has strict rules for meal safety and restaurant hygiene, and has been working closely with mainland officials to make sure all safety measures are followed.
