MIDDLE TENNESSEE MEDICAL CENTER
TOPIC: Understanding & Preventing Infectious Disease
Monday, November 21, 2011
Rakesh Kumar, MD: infectious disease specialist
News notes via www.webmd.com
Understanding MRSA Infection -- the Basics
What Is MRSA?
Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that causes infections in different parts of the body. It's tougher to treat than most strains of staphylococcus aureus -- or staph -- because it's resistant to some commonly used antibiotics.
The symptoms of MRSA depend on where you're infected. Most often, it causes mild infections on the skin, causing sores or boils. But it can also cause more serious skin infections or infect surgical wounds, the bloodstream, the lungs, or the urinary tract.
Though most MRSA infections aren't serious, some can be life-threatening. Many public health experts are alarmed by the spread of tough strains of MRSA. Because it's hard to treat, MRSA is sometimes called a "super bug."
What Causes MRSA?
Garden-variety staph are common bacteria that can live on our bodies. Plenty of healthy people carry staph without being infected by it. In fact, 25%-30% of us have staph bacteria in our noses.
But staph can be a problem if it manages to get into the body, often through a cut. Once there, it can cause an infection. Staph is one of the most common causes of skin infections in the U.S. Usually, these are minor and don't need special treatment. Less often, staph can cause serious problems like infected wounds or pneumonia.
Staph can usually be treated with antibiotics. But over the decades, some strains of staph -- like MRSA -- have become resistant to antibiotics that once destroyed it. MRSA was first discovered in 1961. It's now resistant to methicillin, amoxicillin, penicillin, oxacillin, and many other antibiotics.
While some antibiotics still work, MRSA is constantly adapting. Researchers developing new antibiotics are having a tough time keeping up.
Who Gets MRSA?
MRSA is spread by contact. So you could get MRSA by touching another person who has it on the skin. Or you could get it by touching objects that have the bacteria on them. MRSA is carried, or "colonized," by about 1% of the population, although most of them aren't infected.
MRSA infections are common among people who have weak immune systems and are in hospitals, nursing homes, and other heath care centers. Infections can appear around surgical wounds or invasive devices, like catheters or implanted feeding tubes. Rates of infection in hospitals, especially intensive care units, are rising throughout the world. In U.S. hospitals, MRSA causes more than 60% of staph infections.
Community-Associated MRSA (CA-MRSA)
But MRSA is also showing up in healthy people who have not been living in the hospital. This type of MRSA is called community-associated MRSA, or CA-MRSA. The CDC reports that in 2007, 14% of people with MRSA infections had CA-MRSA.
Studies have shown that rates of CA-MRSA infection are growing fast. One study of children in south Texas found that cases of CA-MRSA had a 14-fold increase between 1999 and 2001.
CA-MRSA skin infections have been identified among certain populations that share close quarters or experience more skin-to-skin contact. Examples are team athletes, military recruits, and prison inmates. However, more and more CA-MRSA infections are being seen in the general community as well, especially in certain geographic regions.
It's also infecting much younger people. In a study of Minnesotans published in The Journal of the American Medical Association, the average age of people with MRSA in a hospital or health care facility was 68. But the average age of a person with CA-MRSA was only 23.
Are Gyms Hotbeds of MRSA Infections? Maybe Not
Study Suggests Gym Surfaces Have an Unfair Reputation as Sources of MRSA
By Denise Mann
WebMD Health News
March 4, 2011 -- Gym surfaces were thought to be likely hosts for the superbug MRSA, but a new study shows that this risk may be exaggerated.
In addition, the study shows the risk of MSSA (methicillin-sensitive Staphylococcus aureus) infections from gym surfaces may also be exaggerated.
The findings appear in the March issue of the American Journal of Infection Control.
MRSA is formally known as methicillin-resistant Staphylococcus aureus. Antibiotic-resistant staph infections like MRSA infections largely occur in hospitals and health care settings, but rates of these infections have been climbing, which has led to concern that community gyms could be hotbeds.
MRSA can live on dry surfaces for long periods. As a result, many gyms have initiated extensive clean-up programs and offer antiseptic wipes to members to clean off equipment before and after use.
Looking for MRSA in Gyms
Researchers tested 240 samples taken from gym mats, dumbbells, and cardio and weight machines at three community-based gyms before and after cleaning at three times during the day. None of these samples tested positive for MRSA or MSSA.
Study researcher Kathleen Ryan, MD, a pediatrician at University of Florida College of Medicine in Gainesville, says she was surprised that they found no evidence of MRSA/MSSA at these gyms.
The study is by no means the final word, she says. "We still need to be cautious, but we don't need to be paranoid that everything we touch is going to potentially infect us."
"Wiping down mats and pieces of equipment and keeping your hands clean is enough," she says. MRSA is more likely to spread from skin-to-skin, as opposed to skin-to-surface contact.
"Don't slack off, but we can feel comfortable that when we go to gym, we can work out and not have to be worried about MRSA/MSSA infection," she says.
Don't Share Equipment
Philip M. Tierno Jr., PhD, director of clinical microbiology and immunology at the New York University Langone Medical Center and a clinical professor of microbiology and pathology at the New York University School of Medicine in New York City, has also tested gym surfaces for MRSA.
"The only place where there was MRSA was on a medicine ball," he says. Other bacteria were found, including the more mild Staphylococcus epidermidis, he says.
"It is not unusual to go to three locations and not find any MRSA. But had they cultured 10 gyms they may have found MRSA/MSSA," he says.
Tierno says he is curious what type of bacteria, if any, they did find. Ryan tells WebMD that her team only looked for MRSA/MSSA and does not have data on what other bacteria may lurk on the surfaces at local gyms.
MRSA/MSSA is most often transmitted when people share equipment, helmets, uniforms, towels, and shoes, Tierno says.
If you want to avoid MRSA/MSSA, "don't share things," he says.
MRSA: Worse in the Community Than the Hospital?
Drug-resistant staph infections caught in the community may be more dangerous than those found in hospitals, according to a new study.
Researchers found the community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) bacterium secretes agents that attract and destroy immune cells that are supposed to protect against infection.
CA-MRSA infection is a global health issue because new strains of these staph bacteria have become resistant to treatment with many antibiotics and can cause severe infection in otherwise healthy individuals.
Although much attention has been paid to the hospital-associated strains of the bacterium, researchers say the findings show that the strains in the community may be more serious and difficult to treat.
New Clues on MRSA
In the study, Michael Otto, PhD, and colleagues at the National Institute of Allergy and Infectious Diseases' (NIAID) Rocky Mountain Laboratories identified peptides (building blocks of protein) called PSM that are secreted by CA-MRSA. The results appear in Nature Medicine.
These peptides appear to destroy healthy immune cells that would normally fight against the infection.
Researchers developed test strains of CA-MRSA based on widespread strains of the bacterium, identified the PSM genes within them, and performed lab tests on mice.
The results showed that the gene cluster responsible for production of PSM proteins played a critical role in the bacterium's ability to produce disease by attracting and then destroying important immune cells. Researchers say this group of genes may not be the only element affecting CA-MRSA disease severity, but it plays a major role.
They also compared PSM production from CA-MRSA with hospital-associated MRSA and found that the CA-MRSA produced more PSMs in lab tests.
"This elegant work helps reveal the complex strategy that S. aureus has developed to evade our normal immune defenses," says Anthony S. Fauci, MD, director of the NIAID. "Understanding what makes the infections caused by these new strains so severe and developing new drugs to treat them are urgent public health priorities."