Percent of patients exposed to infected prior bed occupants and roommates in controls versus cases having healthcare-associated infections with Staphylococcus aureus, Acinetobacter baumannii, Streptococcus pneumoniae, Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterococcus faecalis, and Enterococcus faecium exposed to prior bed occupants and roommates infected or colonized with the same organism.