Trends in Streptococcus pneumoniae Antibiotic Susceptibility at George Washington University Hospital, 2000-2015

Background: The trends in susceptibility of Streptococcus pneumoniae isolates to commonly used antibiotics of local and national health interest. We investigated trends in S. pneumoniae antimicrobial susceptibility over a 16-year period at the George Washington University Hospital (GWUH) and compared our results to national data from the CDC: Active Bacterial Core Surveillance Report for S. pneumoniae.

Methods: Antibacterial minimum inhibitory concentrations to 9 antibiotics were determined using the E-test® procedure, according to the Clinical and Laboratory Standards Institute (CLSI) 2015 Performance Standards for Antimicrobial Susceptibility Testing. CLSI interpretive standards for non-meningitis and meningitis breakpoints were used as applicable. Susceptibility patterns were analyzed in blocks spanning 2000 to 2003 (block A), 2004 to 2007 (block B), 2008 to 2011 (block C) and 2012 to 2015 (block D).

Results: 568 S. pneumoniae isolates were collected over the 16-year study period from sterile (CSF, blood) and nonsterile (respiratory, wound) sites. The number of isolates has steadily declined from 172 isolates in Block A to 90 isolates in Block D. From Block A to C, ceftriaxone susceptibility decreased from 99.4% to 91.6%, clindamycin from 92.1% to 77.1%, and erythromycin from 79.4% to 66.7% but rose to 92.1%, 85.7% and 75.3% for these antibiotics respectively in Block D. Only susceptibility to penicillin G continued to fall from 79.8% in Block A to 68.9% in Block D. 99.7% of all isolates over the study period were susceptible to levofloxacin, 99.8% to moxifloxacin and 100% to vancomycin. Multi-drug (≥ 2 antibiotics) resistance increased from 11.0% of isolates in block A to 23.7% in block C, but decreased to 13.3% in block D.

Conclusion: Similar to national surveillance date, S. pneumoniae susceptibility to ceftriaxone, erythromycin, and clindamycin at GWUH has improved over the last 4 years. However, our penicillin sensitivity continues to decline, which is at odds with national surveillance data where penicillin susceptibility improved from 76% in 2007 to 94.7% in 2014. Importantly, there has been a decline in multi-drug resistance in the last 4 years.