ROC_AUC curve for performance of a classification

I am doing LEfSe analysis between three sample types(control, asymptomatic and symptomatic) in genus level taxa. And from LEfse results, taken all those bacteria and trying to do ROC AUC to determine classification performance. when I am compared symptomatic and asymptomatic groups, getting fair AUC percentage (76.6%) but when trying to compared with control group getting AUC 100%.I want clarify on this point, is it possible to get AUC 100%