Staphylococcus aureus(S. aureus) is a common bacteria. Many healthy people have it on their skin or in their noses. Occasionally it causes infections. Most are minor skin infections, such as pimples and boils. However, S. aureus can cause serious infections, such as pneumonia, septicemia (bloodstream infection), and wound infections. The serious infections most often occur in people with depressed immune systems, recent surgery, long-term dialysis, or recent hospitalization for a major illness. People in these situations have increased risks for the serious S. aureus infections if they have S. aureus in their noses. Doctors know that rubbing antibiotic ointment inside the nose helps rid it of S. aureus bacteria. But they don't know whether giving the antibiotic nose ointment actually prevents serious S. aureus infections.