Antibiotics contribute to spread of MRSA in hospitals

Published: 21-Sep-2012

London University study also finds improved hand hygiene has only a small effect on MRSA reduction


The use of a commonly prescribed antibiotic, ciprofloxacin, is a major contributor to the spread of infection in hospitals by methicillin-resistant Staphylococcus aureus (MRSA), according to new research.

The study, led by a team at St George’s, University of London, 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.

The team tracked MRSA infection 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 drop 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 70–100 daily doses for every 1,000 occupied beds to about 30 doses. In the same period, the number of patients identified by the laboratory to be infected with MRSA fell by 50%, from an average of about 120 a month to about 60. Following this, over the last two years of the study both the drug prescription level 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 could have contributed to this decrease in infection. During a four-year period when more stringent infection control policies were introduced – including improved cleaning and hand washing, and screening patients for MRSA on arrival at hospital – the only major reduction in MRSA infection rates coincided with the reduction in ciprofloxacin prescriptions.

Lead author Jodi Lindsay, a reader in microbial pathogenesis at St George’s, University of London, said: ‘Surprisingly, it wasn't hygiene and hand washing that were the main factors responsible for the decrease in MRSA in the hospital. Rather, it seemed to be a change in the use of a particular group of antibiotics. Hand washing and infection control are important, but they were not enough to cause the decrease in MRSA we saw.’

Lindsay said the study suggested that MRSA relies on ciprofloxacin – and fluoroquinolones in general – to thrive in hospitals, as well as penicillin-type drugs, which was already assumed. The fluoroquinolone group of antibiotics have a similar enough mechanism of action to assume that the effect would be the same for them all.

She added that the findings suggest the most effective way to control MRSA and other hospital-based superbugs is to continue seeking alternative ways to use antibiotics, rather than simply focusing on infection control techniques.

As well as identifying factors that influenced prevalence, the researchers discovered that the CC22 strain of MRSA has become the dominant type. It has thrived by developing and maintaining multi-drug resistance, and becoming more fit to survive on hospital surfaces than other strains.

Lindsay said studying the dynamic of how MRSA bacteria strains continue to evolve in hospitals in response to changing practice and interventions, such as infection control and antibiotic prescribing, will be essential in determining which interventions work, which are cost effective, and which are likely to have the best long-term outcomes.

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