Antimicrobial resistance leads to increased healthcare costs primordially due to a higher morbidity and mortality from infectious diseases, and increased length of hospital stay. The relationship between antimicrobial consumption and antimicrobial resistance is complex and remains far from fully understood. The objective of the present study was to investigate the relationship between the average daily intake of antimicrobial agents and the occurrence of microbial drug resistant organisms, in particular well known pathogens, at the individual patient level both in the ambulatory and in the in-patient setting. The microbiological results of voluntary participating clinical laboratories during 2005 were coupled with the antimicrobial consumption patterns (July 2004- December 2005) as provided by the pooled data of the seven Belgian health insurance funds (intermutualistic agency). Univariate and multivariate logistic regression were used to identify risk factors for antimicrobial resistance following antimicrobial consumption and other patient characteristics (calculation of Odd’s Ratios). A total of 105,198 samples, originating from 16 laboratories and 44,365 patients matched the criteria for further analysis through subsets of combinations of microorganisms and susceptibility profiles. Herein only the first isolate per patient was retained so as to minimize confounding through underlying disease and/or severity of infection. For Staphylococcus aureus, coagulase negative staphylococci, Escherichia coli, and Klebsiella pneumoniae, strong significant relationships (p<0.001) were found between their resistance profiles and the individual consumption of antimicrobial agents expressed as defined daily doses (DDD). This was especially the case for older and newer beta-lactam antibiotics (incl. cephalosporins) and for fluoroquinolones. These three groups of antimicrobial agents counted for 63.45% of total antimicrobial consumption within the study population. For Streptococcus pneumoniae, resistance to penicillines was increased by the use of the group of macrolides, lincosamides and streptogramines. These data strongly support the existence of a risk for acquired antimicrobial resistance in major bacterial pathogens, directly related to the consumption of antimicrobial agents at the individual patient level. When prescribing these agents of vital importance, clinicians should consider that antimicrobial consumption also inherently bears an individual risk for their own patient, besides the resistance induction at the population level that has been known for a long time.
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