MRSA prevalence may be due to over-prescribing and overuse of antibiotics

A dangerous drug-resistant bacterium is becoming more prevalent in many intensive care units, according to an article in the Feb. 1 issue of Clinical Infectious Diseases, now available online.

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for a variety of infections that patients often acquire in the hospital. Skin infections are the most common, but MRSA can also infect the heart, the lungs, and the digestive tract. The emergence of MRSA and other drug-resistant bacteria may be due in part to over-prescribing and overuse of antibiotics.

Researchers at the Centers for Disease Control and Prevention examined MRSA data from more than 1,200 intensive care units (ICUs) from 1992 to 2003. They found that in 1992, 36 percent of S. aureus isolates were drug-resistant; but in 2003, 64 percent of isolates were MRSA, an increase of about 3 percentage points per year.

Despite the increase in MRSA prevalence, there was also a decrease in MRSA that was resistant to multiple drugs. The researchers hypothesize that the influx of MRSA strains from the community might have replaced those multidrug-resistant strains associated with the hospital.

"Unlike traditional MRSA the community strain is very fit - it causes infection in healthy people," said CDC epidemiologist Dr. Monina Klevens. "When it is introduced into a hospital, where ill patients are more vulnerable to infection, it has the potential to cause significant morbidity and mortality."

Due to community MRSA's ability to infect the young and healthy, traditional risk factors for identifying hospital-associated MRSA colonization, such as dialysis and prior hospitalization, are not effective predictors of whether a person is carrying the community strain.

"Lines are blurring as far as risk factors are concerned," Dr. Klevens said.

The study summarized MRSA data at the national level, indicating general trends, but physicians need to know what is happening in their specific locations to help control the spread of infection.

"We know that the prevalence of community MRSA varies widely in local geographic areas, so it is important that doctors be aware of what is happening in their community," Dr. Klevens said.