Clostridium difficile has surpassed methicillin-resistant Staphylococcus aureus (MRSA) as Microbial Enemy No. 1 in America's hospitals. This bug can cause severe, often life threatening colitis, is increasingly common and more virulent than it used to be. Overuse of antibiotics is a main driver of the epidemic, and public health leaders are calling on community based physicians to be extremely judicious in their use of antibiotics.