What Causes Strong Stool Odor In An Alcoholic?

I know stool is supposed to smell not good normally, but my grandfather's stool smells extremely bad. I used the bathroom at my grandparents house once after he did, and the smell was atrocious. I could taste the smell and I was gagging. I have a very strong stomach but the smell made me gag, and when I was away from the bathroom I felt like the smell had stuck to me, it was by far the worst thing I have every smelled. My grandfather is 71 years old and an alcoholic. Is this atrocious smelling bowel a sign of something I should be worried about? Is this normal? Why is this happening?