Link to the published article is present within the article, which I always appreciate.

Based on a cursory read of the methods, they included socioeconomic status as a covariate, which is always the first thing I check in similar articles. However, they only consider the mother's cleaning habits, which I find surprising.

Growing up with firearms, my dad was always the one maintaining the guns. He was the vector for any exposure to contaminants. My dad was also a neat freak. I would have liked to have seen the researchers consider the father's cleanliness factor. EDIT: if it was present in the epidemiological data, it may have correlated with safe storage. Clean dads are more likely to store their guns safely, I bet.