Is door opening to more strep pneumo resistance?

Fluoroquinolone resistance a foreboding sign

Emerging resistance to fluoroquinolones in Streptococcus pneumoniae is raising concerns that it will become increasingly difficult to battle strains of the bug already resistant to penicillin and other antibiotics.

A recent study found that the increase in the use of fluoroquinolones in Canada has been associated with a corresponding rise in the frequency and degree of reduced susceptibility to fluoroquinolones in penicillin-resistant S. pneumoniae.¹ That finding is all the more concerning when one considers that fluoroquinolone use in general has only increased since the research was conducted, says co-author Allison McGeer, MD, director of infection control at Mount Sinai and Princess Margaret Hospitals in Toronto.

"We were sitting, if you like, with just a crack in the door in terms of the kind of pressure we were applying to strep pneumo," she tells Hospital Infection Control. "What we have done is open the door wide open. We have a whole bunch of new quinolones that are great against pneumococcal infections. People are going to use them to treat pneumonia. We are about to dramatically step up the pressure that is applied to strep pneumo. The concern, of course, is if this is what you can do with a decade or less of indirect, fairly low-grade pressure, what is going to happen with three or four years of really high-grade pressure?"

Fluoroquinolones are now recommended for the treatment of respiratory tract infections due to S. pneumoniae, particularly when the isolates are resistant to beta-lactam antibiotics. McGeer and colleagues performed susceptibility testing on 7,551 isolates of S. pneumoniae obtained from surveillance in Canada in 1988 and from 1993 to 1998. They found that between 1988 and 1997, fluoroquinolone prescriptions increased from 0.8 to 5.5 per 100 persons per year. The prevalence of pneumococci with reduced susceptibility to fluoroquinolones increased from 0% in 1993 to 1.7% in 1997 and 1998. Among adults, the prevalence increased from 1.5% in 1993 and 1994 combined to 2.9% in 1997 and 1998 combined.

Although there is increasing evidence that antimicrobial resistance is directly related to increased antimicrobial use, some question the need for concern about fluoroquinolones, because after 15 years of clinical use, there have been only occasional reports of pneumococci with reduced susceptibility, the authors concluded. However, the development of reduced susceptibility to fluoroquinolones requires sequential mutations, and one might thus expect a substantial delay between the introduction of fluoroquinolones and the appearance of clinically significant reductions in susceptibility, they warn. Reduced susceptibility was found in various clones and serotypes, suggesting that new resistance is developing in multiple indigenous strains. The results suggest selective antibiotic pressure applied to many strains simultaneously may be at the root of the emerging resistance.

Reference

1. Chen DK, McGeer A, De Azavedo JC, et al. Decreased susceptibility of Streptococcus pneumoniae to fluoroquino lones in Canada. N Engl J Med 1999; 341:233-239.