Is living in a house with a sister infected with hand foot and mouth disease dangerous for me?

Depends on situation: If you had the viruses before that cause the disorder you will be immune. If you are susceptible but are cautious & have no contact with the saliva of the person you are at low risk. It occurs most often in kids under 5 but we see occasional strains affect adults. I would not consider it much of a threat to any adult who is not immune compromised by chronic illness or chemo.