Impact of the new CLSI non-meningitis penicillin breakpoints on the reporting of antimicrobial susceptibility in pneumococcal infections

Abstract number: P600

Su L-H., Chiu C-H., Wu T-L., Kuo A-J., Sun C-F.

Objectives: The present breakpoints for defining the susceptibility of meningeal pneumococcal isolates to cefepime, cefotaxime, and ceftriaxone are different from those for nonmeningeal pneumococcal isolates due to the attainability of these agents in the cerebral spinal fluids. However, although the penicillin breakpoints were defined based upon measured penicillin concentrations in the cerebral spinal fluids after intravenous infusions and upon meningitis treatment failures, the breakpoints have been applied to nonmeningeal pneumococcal isolates since the definitions were developed in the late 1970s. In 2008, a new set of breakpoints will be published by the CLSI to be used for defining the penicillin susceptibility of nonmeningeal pneumococcal isolates. The present report aimed to assess the impact of the new breakpoints on the reporting of pneumococcal susceptibilities.

Methods: The MICs of penicillin to pneumococcal isolates were examined by the standard broth microdilution method as recommended by the CLSI. The results between 2000 and June 2007 were collected and analysed against both of the old (susceptible, leqslant R: less-than-or-eq, slant 0.06 mg/L; intermediate, 0.12–1 mg/L; resistant, geqslant R: gt-or-equal, slanted 2 mg/L) and new (susceptible, leqslant R: less-than-or-eq, slant 2 mg/L; intermediate, 4 mg/L; resistant, geqslant R: gt-or-equal, slanted 8 mg/L) definitions.

Results: Results from a total of 3156 pneumococcal isolates, including 1.1% of meningeal isolates, were available for analysis. With the old definition, the rate of penicillin nonsusceptibility increased from 88.6% in 2000 to 92.9% in 2007 (average, 91.2%). With the new definition, the rate of penicillin nonsusceptibility decreased from 34.5% in 2000 to 2.5% in 2007 (average, 20.4%). Notably, the proportion of isolates with the MICs of 1–2 mg/L increased significantly from 41.4% in 2000 to 70.7% in 2007.

Conclusions: Application of the new breakpoints will result in a significantly lower rate of penicillin nonsusceptibility in nonmeningeal pneumococcal isolates. Clinicians may feel more confident in using penicillin for the treatment of pneumococcal infections, and thus the use of other advanced drug classes may be exempted. However, as the population of pneumococcal isolates with borderline penicillin susceptibility (MIC, 1–2 mg/L) is increasing, the regimen of penicillin treatment must be closely monitored to achieve a satisfied therapeutic outcome.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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