“Although we have not been advised that it is necessary or advisable for us to cancel the exchange for medical or public health reasons, I make this decision because of the following factors,” Darryl J. Ford wrote in the letter, posted on 6ABC’s website. He cited parent and student concern, the disruption to the educational program, uncertainty about when the school will learn about the test results, the media presence Monday at the school, and reports citing the Chinese government as saying the virus can be spread even though a person is not showing symptoms.