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Use of Common Antibiotic Aids Spread of MRSA in Hospitals, Study Finds

“Super bug” appears to thrive on ciprofloxacin (Sept. 20)

The use of a commonly prescribed antibiotic is a major contributor to the spread of infection in hospitals by the “super bug” methicillin-resistent Staphylococcus aureus (MRSA), according to new research announced on September 20 by St. George’s University of London. The study also found that increasing measures to prevent infection, such as improved hygiene and hand washing, appeared to have only a small effect on reducing MRSA infection rates during the study period.

MRSA is a bacterium that causes hospital-acquired infection and is resistant to all of the penicillin-type antibiotics frequently used in hospitals to prevent and treat infection. It can cause serious infections of the skin, blood, lungs and bones.

The researchers tracked MRSA infection over 10 years (from 1999 to 2009) at St. George’s Hospital, looking at how it has adapted to survive in a hospital environment and at factors that affected its prevalence. They found that a significant decrease in MRSA rates coincided with a reduction in hospital prescriptions of ciprofloxacin, the most commonly prescribed antibiotic of the fluoroquinolone family.

Over a short period of the study, ciprofloxacin prescriptions fell from 70 to 100 daily doses for every thousand occupied beds to about 30 doses. During the same period, the number of patients identified by the laboratory as infected with MRSA fell by half, from an average of about 120 a month to about 60 a month. Over the last 2 years of the study, both drug prescriptions and MRSA rates remained at these reduced levels.

The study, published in the Journal of Antimicrobial Chemotherapy, looked at whether other factors, such as improved infection-control measures, may have contributed to the decrease in infection. However, during a 4-year period when more stringent infection-control policies were introduced — including improved cleaning and hand washing, and screening patients for MRSA on arrival at the hospital — the only major reduction in MRSA infection rates coincided with the reduction in ciprofloxacin prescriptions.

According to lead author Dr. Jodi Lindsay, the study suggested that MRSA relies on ciprofloxacin — and fluoroquinolones in general — to thrive in hospitals, as well as on penicillin-type drugs, which was already assumed. The mechanisms of action of the fluoroquinolone group of antibiotics are sufficiently similar to assume that the effect would be the same for all of them, Lindsay added.

The findings suggest that the most effective way to control MRSA and other hospital-based “super bugs” is to continue finding alternative ways to use antibiotics, rather than simply focusing on infection-control techniques, Lindsay said.

For more information, visit the St. George's University of London Web site.

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