A study carried out over a decade in a single hospital suggests that reducing the use of fluoroquinolones is essential to reducing MRSA infection rates.
A sharp reduction in the prescription of the antibiotic ciprofloxacin led to a similarly sharp reduction in the rate of methicillin-resistant Staphylococcus aureus
(MRSA) infection among patients at a hospital in the United Kingdom, according to the results of a study
published online on July 3, 2012, in the Journal of Antimicrobial Chemotherapy
. The study also found that stricter infection control measures failed to reduce the rate of MRSA infection.
The researchers studied MRSA infection at St. George’s Hospital in London from 1999 to 2009. The total rate of antibiotic prescription changed little over the 10-year duration of the study. However, in 2007, a policy of reduced prescription of ciprofloxacin and cephalosporins was introduced. Over a short period, the hospital’s rate of ciprofloxacin prescription fell from 70-100 daily doses to approximately 30 daily doses for each 1000 occupied beds. Over the same period, the number of patients in the hospital with MRSA fell from approximately 120 per month to approximately 60 per month. For the remaining 2 years of the study, the ciprofloxacin prescription level and the MRSA infection rate remained steady.
From 2005 through 2009, other measures were also introduced at the hospital to reduce infection with MRSA and other hospital-associated infections, such as Clostridium difficile
. These included hand washing, education, hospital cleaning, behavioral changes, and improved line-care. These measures failed to reduce the rate of MRSA infection.
Specific infection control strategies geared toward MRSA were also introduced, such as screening newly admitted patients for MRSA and decolonization of MRSA-positive patients with chlorhexidine washes and by applying mupirocin ointment to the nose and minor wounds. However, increased prescription of mupirocin did not coincide with decreased MRSA infection rates, nor did a 2005 policy to reduce the length of patient stays in the hospital.
The researchers note that other antibiotics in the same family as ciprofloxacin, the fluoroquinolones, have sufficiently similar mechanisms of action that they would most likely have a similar effect in terms of increasing MRSA infection rates. They suggest that developing alternative ways of using antibiotics is key to controlling MRSA.
"Surprisingly, it wasn't hygiene and hand washing that were the main factors responsible for the decrease in MRSA in the hospital,” said Jodi Lindsay, PhD, the lead study author and a professor of microbial pathogenesis at St. George’s, University of London, in a press release. “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."
Dr. Lindsay and her colleagues also looked at the different clones of MRSA that circulated in the hospital during the study period. They found that 3 clones caused the majority of all infections and that clones that were resistant to multiple drugs tended to dominate. No individual sample of MRSA was completely drug resistant, and a given clonal group tended to gain and lose resistance to different drugs over time. The exception, however, was fluoroquinolone resistance, which was rarely lost by any of the dominant clones in the hospital, suggesting that this resistance contributes to the selection and survival of hospital-acquired MRSA.