What is Staphylococcus aureus?

Staphylococcus aureus, often simply referred to simply as "staph", are bacteria commonly found on the skin and in the noses of healthy people. Occasionally, staph can cause infection; staph bacteria are one of the most common causes of skin infections in the United States. Most of these infections are minor (such as pimples, boils, and other skin conditions) and most can be treated without antimicrobial agents (also known as antibiotics or antibacterial agents). However, staph bacteria can also cause serious and sometimes fatal infections (such as bloodstream infections, surgical wound infections, and pneumonia). In the past, most serious staph bacterial infections were treated with a type of antimicrobial agent related to penicillin. Over the past 50 years, treatment of these infections has become more difficult because staph bacteria have become resistant to various antimicrobial agents, including the commonly used penicillin-related antibiotics.

What are VISA and VRSA?

VISA and VRSA are specific types of antimicrobial-resistant staph bacteria. While most staph bacteria are susceptible to the antimicrobial agent vancomycin some have developed resistance. VISA and VRSA cannot be successfully treated with vancomycin because these organisms are no longer susceptibile to vancomycin. However, to date, all VISA and VRSA isolates have been susceptible to other Food and Drug Administration (FDA) approved drugs.

How do VISA and VRSA get their names?

Staph bacteria are classified as VISA or VRSA based on laboratory tests. Laboratories perform tests to determine if staph bacteria are resistant to antimicrobial agents that might be used for treatment of infections. For vancomycin and other antimicrobial agents, laboratories determine how much of the agent it requires to inhibit the growth of the organism in a test tube. The result of the test is usually expressed as a minimum inhibitory concentration (MIC) or the minimum amount of antimicrobial agent that inhibits bacterial growth in the test tube. Therefore, staph bacteria are classified as VISA if the MIC for vancomycin is 4-8µg/ml, and classified as VRSA if the vancomycin MIC is >16µg/ml.

How common are VISA and VRSA infections?

VISA and VRSA infections are rare. Only sixteen cases of infection caused by VISA (Michigan 1997, New Jersey 1997, New York 1998, Illinois 1999, Minnesota 2000, Nevada 2000, Maryland 2000, and Ohio 2001) and six cases of infection caused by VRSA (Michigan 2002 , Pennsylvania 2002, New York 2004, and 3 from Michigan in 2005) have been reported in the United States.

Who gets VISA and VRSA infections?

Persons that developed VISA and VRSA infections had several underlying health conditions (such as diabetes and kidney disease), previous infections with methicillin-resistant Staphylococcus aureus (MRSA), tubes going into their bodies (such as intravenous IV catheters), recent hospitalizations, and recent exposure to vancomycin and other antimicrobial agents.

What should I do if I think I have a Staph, MRSA, VISA, or VRSA infection?