Changes in antimicrobial susceptibility of blood isolates in a university hospital in South Korea, 1998-2010

Background: Local epidemiologic data on prevalent pathogens are important to guide empirical antibiotic therapy. In this study, we observed annual changes in frequency of occurrence and in vitro antimicrobial susceptibility of blood isolates over a period of 13 years. Materials and Methods: We reviewed blood isolates identified during the period from 1998 to 2010 at Seoul National University Hospital. Only first isolates for each patient were included in the analysis. We analyzed the frequency of isolates and their trend with regard to in vitro antimicrobial susceptibility. Data were presented according to guidelines of the Clinical and Laboratory Standards Institute (CLSI) (2009). Results: A total of 23,501 isolates were identified during the period from 1998 to 2010. Fifty-five percent of the isolates were gram-positive cocci, 38% were gram-negative rods, and 3% were fungi. Coagulase-negative Staphylococcus (CoNS) (24%), Escherichia coli (16%), Staphylococcus aureus (10%), and Klebsiella pneumoniae (8%) were the most commonly isolated bacteria, and Candida albicans (2%) was the most commonly isolated fungus. The frequency of CoNS increased from 18.0% to 26.8%, whereas the frequency of E. coli and K. pneumoniae decreased from 20.2% to 13.7% and from 11.7% to 6.7%, respectively. Overall, the proportion of methicillin-resistant S. aureus changed from 47.9% to 62.1%. In E. coli, the resistance rate of cefotaxime and ciprofloxacin increased over a period of 13 years. However, such an increase of resistance was not observed in K. pneumoniae. In P. aeruginosa, and particularly in A. baumannii, resistance to imipenem rose alarmingly (3% in 1998 to 27.8% in 2010, 5% in 1998 to 68.9% in 2010, respectively). Conclusions: Over the last 13 years, the proportion of CoNS in blood isolates increased, which led to a relative decrease of isolated gram-negative rods. Proportions of MRSA showed no significant change, whereas cefotaxime resistant and ciprofloxacin resistant E. coli increased. Imipenem resistant P. aeruginosa and A. baumannii also increased during the study period.