Staph Infection
(Staphylococcus Aureus)
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
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Superbug Staph Spread in Community
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor:
Barbara
K. Hecht, PhD
 MRSA, or methicillin-resistant Staphylococcus aureus, is a bacterium that can
cause serious infections. It is resistant to numerous antibiotics of the
beta-lactam family, including methicillin and penicillin.
MRSA belongs to the large group of bacteria known as
Staphylococci, often referred to as Staph. About 25%-30% of all people have Staph
within the nose, but it normally does not cause an infection. In contrast, only about 1% of the
population have MRSA.
Infections with MRSA are most common in
hospitals and other institutional health-care settings, such as nursing homes,
where they tend to strike older people, those who are very ill, and people with a
weakened immune system. In health-care settings, MRSA is a frequent cause of
surgical wound infections, urinary
tract infections, bloodstream infections (sepsis), and pneumonia.
MRSA outbreaks, however, are appearing increasingly in the
community. Infections can occur in people who have not been hospitalized or had a
medical procedure performed in the past year, and who do not have immune
deficiency. These infections are termed community-associated MRSA infections
(CA-MRSA).
The U.S. Centers for Disease Control and Prevention (CDC) estimates that about 12% of
MRSA infections are now community-associated, but this percentage can vary by
community and patient population.
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What is Staphylococcus?
Staphylococcus is group of bacteria, familiarly known as Staph (pronounced "staff"), that can cause a multitude of diseases as a result of infection of various tissues of the body. Staph bacteria can cause illness not only directly by infection (such as in the skin), but also indirectly by producing toxins responsible for food poisoning and toxic shock syndrome. Staph-related illness can range from mild and requiring no treatment to severe and potentially fatal.
The name "Staphylococcus" comes from the Greek staphyle meaning a bunch of grapes and
kokkos meaning berry, and that is what Staph look like under the microscope, like a bunch of grapes or little round berries. (In technical terms, these are gram-positive, facultative anaerobic, usually unencapsulated cocci.)
Over 30 different types of Staphylococci can infect humans, but most infections are caused by
Staphylococcus aureus. Staphylococci can be found normally in the nose and on the skin (and less commonly in other locations) of 20%-30% of healthy adults. In the majority of cases, the bacteria do not cause disease. However, damage to the skin or other injury may allow the bacteria to overcome the natural protective mechanisms of the body, leading to infection.
Who is at risk for Staph infections?
Anyone can develop a Staph infection, although certain groups of people are at greater risk, including newborn infants, breastfeeding women, and people with chronic conditions such as diabetes, cancer, vascular disease, and lung disease. Injecting drug users, those with skin injuries or disorders, intravenous catheters, surgical incisions, and those with a weakened immune system all have an increased risk of developing Staph infections.
What are the symptoms and signs of a Staph infection?
Staphylococcal disease of the skin usually results in a localized collection of pus, known as an abscess, boil, or furuncle. The affected area may be red, swollen, and painful. Drainage or pus is common.
What types of diseases are caused by Staph?
Staph infections of the skin can progress to impetigo (a crusting of the skin) or cellulitis (inflammation of the connective tissue under the skin, leading to swelling and redness of the area). In rare cases, a serious complication known as scalded skin syndrome (see below) can develop. In breastfeeding women, Staph can result in mastitis (inflammation of the breast) or in abscess of the breast. Staphylococcal breast abscesses can release bacteria into the mother's milk.
When the bacteria enter the bloodstream and spread to other organs, a number of serious infections can occur. Staphylococcal pneumonia predominantly affects people with underlying lung disease and can lead to abscess formation within the lungs. Infection of the heart valves (endocarditis) can lead to heart failure. Spread of Staphylococci to the bones can result in severe inflammation of the bones known as osteomyelitis. Staphylococcal sepsis (widespread infection of the bloodstream) is a leading cause
of shock and circulatory collapse, leading to death, in people with severe burns over large areas of the body.
Staphylococcal food poisoning is an illness of the bowels that causes nausea, vomiting, diarrhea, and dehydration. It is caused by eating foods contaminated with toxins produced by
Staphylococcus aureus. Symptoms usually develop within one to six hours after eating contaminated food. The illness usually lasts for
one to three days and resolves on its own. Patients with this illness are not contagious, since toxins are not transmitted from one person to another.
Toxic shock syndrome is an illness caused by toxins secreted by Staph aureus bacteria growing under conditions in which there is little or no oxygen. Toxic shock syndrome is characterized by the sudden onset of high fever, vomiting, diarrhea, and muscle aches, followed by low blood pressure (hypotension), which can lead to shock and death. There may be a rash resembling sunburn, with peeling of skin. Toxic shock syndrome was originally described and still occurs especially in menstruating women using tampons.
Next: How are Staph infections diagnosed? »
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