Asthma, down on the farm
The hygiene hypothesis got a boost from Ege et al, who analyzed dust from 16,000 European children's bedrooms and mattresses (stored with clinical/demographic data in two huge repositories, GABRIELA and PARSIFAL), for bacterial DNA or growth on bacterial/fungal culture media. Children living on farms had odds ratios for asthma of 0.49 to 0.76, compared to those with no farm exposure. Farm kids' dust had greater diversity of bacterial DNA and more species of bacteria and fungi in cultures, as well. Authors presume the dust was tracked in from barns, fields, etc. NEJM 2011;364:701-709.