An outbreak of norovirus occurred after a church picnic which was attended by 515 persons. Assume everyone ate the same food items. Seventy-five people had fever and diarrhea, 5 of these people were severely affected. Subsequent laboratory tests on all who attended the picnic revealed an additional 65 cases. The attack rate of norovirus was: 14.6% 12.6% 27.2% 15.4% .