A common antibiotic is helping a deadly superbug spread through hospitals, according to research.
Cases of MRSA - a bacteria which causes serious infections of the skin, blood, lungs and bones - decreased when prescriptions of ciprofloxacin were reduced, the University of London study found.
The report also challenged the widely held belief that improved hygiene and hand-washing significantly hinders the spread of the bug.
Researchers led by St George's, University of London, 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 what factors 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.
MRSA, or methicillin-resistant Staphylococcus aureus, causes hospital-acquired infection and is resistant to all of the penicillin-type antibiotics frequently used in hospitals to prevent and treat infection.
Hand-washing and strict hygiene procedures do reduce the spread of the bug, but the St George's study found that they appeared to have only a small effect on lowering MRSA infection rates during the period studied.
During a short period at the hospital, ciprofloxacin prescriptions fell from 70-100 daily doses for every 1,000 occupied beds to about 30 doses. In the same timeframe, the number of patients identified by the laboratory to be infected with MRSA fell by half, from an average of about 120 a month to around 60.
Over the final two years of the study, both the drug prescription level and MRSA rates remained at the reduced levels. It is not known how many of the cases examined in the study were serious.
St George's said the research - 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 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, it said.