

Staph Infections and Methicillin-Resistant Staphylococcus aureus

Print this article
Share this page:
Also known as: Staphylococcus aureus; Staph; Staph aureus; MRSA (pronounced "Mursuh")

What are staph infections?

Staphylococcus aureus, also called S. aureus or "staph," is a bacterium that frequently lives on the human skin without causing illness (colonizes) and is present in the nose of about 25-30% of U.S. adults. S. aureus can exist in this form without causing symptoms or an infection. However, if there is a break in someone's skin from a wound or surgery, or if a person's immune system becomes weakened, then colonizing S. aureus can cause an infection.

Staph frequently causes localized skin infections, such as:

Staph can also cause abscesses and spread to:


Healthcare-associated infections
Staph infections that are acquired while a person is in a hospital, long-term care facility, or other healthcare setting have been a challenge for many years. The confined population and the widespread use of antibiotics have led to the development of antibiotic-resistant strains of S. aureus.

Some of these strains are resistant to methicillin, a type of antibiotic (methicillin-resistant Staphylococcus aureus or MRSA). Infections caused by MRSA are frequently resistant to a wide variety of antibiotics and are associated with significantly higher rates of complications and death (morbidity and mortality), higher healthcare costs, and longer hospital stays than infections caused by methicillin-susceptible S. aureus.

Classic risk factors for MRSA infection in the hospital include surgery, prior antibiotic therapy, admission to an intensive care unit, exposure to a MRSA-colonized patient or healthcare worker, being in the hospital more than 48 hours, and having an indwelling catheter or other medical device that goes through the skin. 

Community-acquired (CA) infections

Investigations of outbreaks have revealed that the CA-MRSA spreads from infected or colonized people to those around them through skin contact (such as sports-related cuts and abrasions), respiratory droplets (sneezing or coughing), or through exposure to contaminated objects (such as shared sports equipment, towels, toys, or playground equipment). Investigations have also revealed that the S. aureus strains involved in CA-MRSA are not the same strains as those that cause healthcare-associated MRSA; they are genetically distinct. The CA-MRSA are resistant to methicillin and related antibiotics (oxacillin, dicloxacillin, nafcillin) and erythromycin but remain susceptible to many other antibiotics.

Next »