Microbiology Testing Has Suboptimal Effect on Antibiotic Stewardship

A small percentage of microbiologic test results are used to direct the antibiotic stewardship processes.

Although many patients with bacterial infections undergo microbiologic testing, a small percentage of these test results are used to direct the antibiotic stewardship processes, according to a study published in the Antimicrobial Resistance and Infection Control.

Researchers of this multicenter cohort study examined the prevalence of microbiology testing and the effect the results have on antibiotic treatment. Data collection occurred at 3 hospitals in Western Norway over a 5 month period. Information on the ordering of microbiologic testing, clinical use of test results, turnaround times of tests, and general clinical and demographic data was recorded.

Of the 1731 patients included in this study, 52% were men, the average age was 68 years, and the length of hospital stay was 6.8 days. These patients were diagnosed with lower respiratory infections (35%), acute exacerbation of chronic obstructive pulmonary disease (24%), sepsis (18%), skin and soft tissue infections (12%), and urinary tract infections (11%). Overall, microbiologic testing was ordered, in accordance with the national antibiotic guidelines, approximately 89% of the time, 76% of tests were blood cultures, 54% were urine cultures, 49% were respiratory tests, and 9% were skin or soft tissue cultures.

Patients often completed more than 1 microbiologic test, regardless of the original diagnosis. The mean turnaround time for blood cultures was 25 hours, 37 hours for urine cultures, 56 hours for skin or soft tissue cultures, and 80 hours for respiratory cultures. Of the 672 microbiologic tests completed at 1 of the hospitals, 358 had negative results, 185 had causative findings, 120 had available, relevant, and causative findings that led to treatment adjustment in 63 (9%) cases.

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Limitations of this study included not incorporating novel technologies that could reduce the turnaround time of culture results, only examining internal medicine departments, and using data originally collected for an antibiotic prescribing intervention study. Future studies are needed to identify ways to decrease the turnaround time of microbiologic testing.

The researchers concluded the “use of microbiology test results to inform antibiotic decision-making needs to be optimized in order to ensure adequate patient treatment and more targeted therapy.”


Skodvin B, Wathne JS, Lindemann PC, et al. Use of microbiology tests in the era of increasing AMR rates — a multicentre hospital cohort study.Antimicrob Resist Infect Control. 2019;8:28.