Just went through something similar on my campus. I had one day with over 25 children on the same grade level and several in other grades inundate the medical room with ILI symptoms. I would have thought I was part of a prank if they didn't each look so miserably ill. Most didn't have a temp over 100.3 but several did. Because of the similarities in symptoms, grade/classroom, volume of students and the fevers, I felt it was reportable.
Unfortunately I didn't find much support initially at the local health department when I contacted them on the same day. There was no protocol for private schools it seems. The initial actions were taken by myself the Principal and VP. I could not find a local public school policy on what to do. I used to work with the dept of health in a large city and while I couldnt contact the person that was in charge of investigating clusters in schools, I went to the CDC website for steps to take.
We notified parents of the increased incidence of student illness and symptoms, what symptoms to look for at home and when to keep kid home and alert their Health care provider. We closed the school and had a company come do a terminal clean. After I faxed the list of students/symptoms to the local health department, I was then transferred to the communicable disease nurse who did find it a reportable cluster and has been great in helping with suggestions going forward. We did end up having 5 cases of flu but it was hard to determine if there were more due to many parents treating symptoms at home.
It's ongoing and there's a ton of communication necessary from the nurses office to parents, administration, staff and then students.