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BACKGROUND: Streptococcus pneumoniae is a gram-positive bacterium that is a common cause of infections including pneumonia and meningitis. In January 2008, the Clinical and Laboratory Standards Institute (CLSI) published revised breakpoints for S. pneumoniae susceptibility to penicillin. Prior to 2008, the susceptible breakpoint was <0.06 µg/mL regardless of body site. The revised guidelines recommend using separate breakpoints for meningitis (<0.06 µg/mL) and non-meningitis (<2.0 µg/mL) isolates for penicillin susceptibility, and reporting them separately on annual antibiograms. The Massachusetts Department of Public Health evaluated the extent to which Massachusetts hospital clinical laboratories followed these CLSI guidelines in 2011.
METHODS: An online survey was sent to microbiology supervisors at 71 acute-care hospitals in Massachusetts. Adherence to CLSI recommendations in reporting S. pneumoniae susceptibility to penicillin was evaluated by the following four measures: (1) the use of different susceptibility breakpoint values for meningitis and non-meningitis infections; (2) breakpoint value used if isolate types were combined; (3) separate reporting of meningitis and non-meningitis isolates on antibiograms; and, (4) breakpoint values used if isolates were separated.
RESULTS: At the time of the initial analysis, surveys were received from 25 acute-care facilities in Massachusetts (35% response rate). Phone interviews are currently being conducted with non-responding hospitals. The initial analysis revealed that: 1) the majority of acute-care hospitals used more than one breakpoint value for penicillin susceptibility to S. pneumoniae (60%). Of those who used one breakpoint for both meningitis and non-meningitis isolates, 50% did so because they did not isolate S. pneumoniae from CSF in 2011. 2) A breakpoint value of <0.06 µg/mL was used by 80% of hospitals applying one breakpoint value. 3) 52% of respondents indicated they separated susceptibility reports for meningitis and non-meningitis isolates on their 2011 antibiogram. 4) Consistent with the 2008 CLSI recommendations, 88% of hospitals reported using a meningitis breakpoint of <0.06 µg/mL and 67% of hospitals reported using a breakpoint of <2.0 µg/mL for non-meningitis isolates.
CONCLUSIONS: In 2008, CLSI published revised susceptibility breakpoints for S. pneumoniae and penicillin based on pharmacokinetic and clinical findings. Analysis revealed that while the majority of hospitals in Massachusetts follow CSLI recommendations, variation in reporting meningitis and non-meningitis breakpoints exists. Given the importance of monitoring antimicrobial resistance, hospital microbiology staff should adhere to CLSI guidelines to ensure consistent measurement of susceptibilities and to allow for standardized analysis of antimicrobial resistance trends.