Antimicrobial susceptibility of Streptococcus pneumoniae at a university hospital in Taiwan, 2000–07: impact of modified

Objectives: In 2008, a new set of penicillin breakpoints was published in the CLSI revised guideline, M100-S18, to define the susceptibility of non-meningeal isolates of Streptococcus pneumoniae. The impact of the change is studied and discussed. Methods: Laboratory data on pneumococcal isolates collected from Chang Gung Memorial Hospital during 2000–07 were analysed using the original and modified penicillin CLSI breakpoints. Results: A total of 3729 non-duplicate isolates were identifed, including 43 (1.2%) meningeal isolates showing high rates of penicillin (79.1%) and ceftriaxone (34.9%) resistance. For non-meningeal iso-lates, penicillin non-susceptibility was reduced significantly from 75.1 % (72.4 % in 2000–03 increasing to 77.4 % in 2004–07) to 16 % (28.6 % in 2000 decreasing to 2.4 % in 2007) if the modified breakpoints were applied. However, isolates for which penicillin MICs were 1–2 mg/L increased significantly from 34.2 % in 2000 to 59.8 % in 2007. Ceftriaxone non-susceptibility also increased significantly from 2.8% before 2005 to 18.4 % thereafter. A quarter (25.7%) of the pneumococcal isolates were recovered from patients <10 years old. Higher resistance to penicillin (89.8 % versus 70.4%; or 19.1 % versus 13.2 % by the modified breakpoints) or ceftriaxone (11.1 % versus 5.8%) was found among these isolates, com-pared with those from older patients