Empirical antibiotic choice alters microbiological outcomes: Findings from comparative antibiograms in a trauma intensive care unit

BACKGROUND: Inappropriate empirical antibiotics promote antibiotic resistance. Antibiograms guide empirical antibiotic therapy by outlining the percentage susceptibility of each pathogen to individual antibiotics. In 2016, the Trauma Intensive Care Unit at Charlotte Maxeke Johannesburg Academic Hospital escalated empirical antibiotic therapy for nosocomial infections from piperacillin-tazobactam to imipenem plus amikacin. OBJECTIVES: This study assessed the impact of escalation in empirical antimicrobial treatment on organism prevalence and resistance profile. METHODS: A retrospective analysis of bacterial and fungal microscopy, culture and susceptibility reports from the laboratory information system of the National Health Laboratory Services, from 1 January 2015 to 31 December 2015 and 1 January 2017 to 31 December 2017, was conducted. Data were de-duplicated according to standard guidelines. Fisher’s exact test was used to determine p-values. RESULTS: Organism prevalence shifted between the years, with a 2.7% increase in streptococci (p=0.0199), 1.7% increase in Candida auris (p=0.0031) and 4.6% and 4.4% reduction in Acinetobacter baumannii (p=0.0508) and Pseudomonas aeruginosa (p=0.0196), respectively. Similarly, there was a change in the resistance profile, with a 28.9% reduction in multi-drug resistant (MDR) A. baumannii (p=0.0001), 60.4% reduction in MDR P. aeruginosa (p=0.0001) and a 6.5% increase in carbapenem-resistant Enterobacterales (p=0.007). The predominant specimen type differed between the years, with significantly more pus, tissue and fluid samples and fewer respiratory samples sent for investigation in 2017 than 2015. CONCLUSION: Escalation in the use of empirical antibiotics showed a change in organism prevalence and an improvement in the susceptibility profile of MDR non-fermenters. CONTRIBUTIONS OF THE STUDY: Current literature on the effects of antibiogram-guided empirical antibiotics is scarce within the South African context. This study shows how antibiograms are an effective antimicrobial stewardship strategy to reduce antimicrobial resistance rates by guiding appropriate choice of empirical antibiotics.