Antimicrobial Stewardship Metrics

Introduction^1-5

The purpose of antimicrobial stewardship (AMS) programs is to ensure appropriate use of antimicrobial agents, improve clinical outcomes, and minimize adverse effects. AMS leaders need to monitor data to satisfy regulatory requirements and to document the impact their programs have on antibiotic use, outcomes, and safety. These metrics can help programs justify costs, incorporate new technologies, or expand. Programs should pick measurements that are relevant and feasible, and an understanding of the types of metrics is critical to prioritization of interventions and distribution of resources. A focus on inpatient AMS metrics is provided below as the optimal metrics in other settings are not well defined.

Types of AMS Metrics^5-9

• AMS metrics are commonly classified as either structural, process, or outcome based.
  
  

Types of Metrics

Structural	Process	Outcome
Leadership and accountability Expertise and resources Policies and programs to improve prescribing Guidelines Education Antimicrobial resistance surveillance and reporting	Document dose, indication, and duration for antibiotic orders Review antibiotics after 48-72 hours (antibiotic time-out) Adherence to treatment guidelines (facility-specific or national) De-escalation frequency Intravenous to oral switch Time to initiation of therapy Time to cessation of antibiotics for surgical prophylaxis Appropriate cultures obtained before antibiotics initiated Acceptance of AMS recommendations Adherence to preauthorization processes Rate of duplicate or redundant therapy	Antimicrobial consumption Length of stay Cure rate Mortality Readmissions Clostridioides difficile infection Adverse drug reactions Antimicrobial resistance Antibiotic cost

Structural Metrics⁵

• Structural indicators are used to evaluate the organization of AMS programs including capabilities, systems, and procedures. Evaluating these does not require many resources  and is a good starting point for new programs. 

• The CDC Core Elements of Hospital Antibiotic Stewardship Programs: Checklist is an example tool that can be used to evaluate the structure of an AMS program.  

Process Metrics^5,7

• Process measures are used to analyze the interventions implemented to improve antibiotic prescribing. Findings from these evaluations can serve as the foundation for future educational efforts or targeted interventions.  

• These metrics range from basic to complex in terms of the time and technology needed to monitor. Programs with limited resources could start by metrics such as adherence to documentation policies for indication, dose, frequency, and duration on all orders. Other more resource intensive metrics, such as adherence to facility-specific treatment guidelines, could be accomplished through a chart review from a sample of patients. 

Outcome Metrics^4,9-11

• Outcome measures are used to demonstrate quantitative changes in patient or economic outcomes. 

• Patient level outcomes are of interest to stakeholders and programs should consider enlisting prescribers to help determine which metrics to monitor. 

• Demonstrating an impact on these outcomes can pose a challenge to programs because patient transfers, comorbid conditions, and other variables make correlation of AMS efforts with these difficult. The collection of these metrics also typically requires manual chart review which may be a barrier to programs with limited resources. 

• Increasing rates of Clostridioides difficile infection (CDI) and multi-drug resistant organisms were the catalyst for the formation of many hospital stewardship programs. Changes in the diagnosis of CDI and potential for community-onset infections have created challenges for demonstrating the impact of AMS interventions on rates of infection. However, most AMS programs collaborate with the infection control and prevention department to track and improve rates of CDI and multi-drug resistant organisms. 

• Many stewardship programs determine the impact of interventions on patient mortality, readmissions, and hospital length of stay. Like other clinical outcomes, there are factors that impact these outcomes that are outside of the control of the AMS team. Including these outcomes in program evaluations is helpful as there is a need to reassure that interventions are not increasing harm. 

• Rates of antibiotic-associated adverse effects such as nephrotoxicity related to use of vancomycin or aminoglycosides is another clinical outcome metric that AMS programs can track. Demonstrating a decrease in the number of patients experiencing these unintended consequences through dose optimization or de-escalation strategies can help justify continued support for AMS activities. 

Antibiotic Consumption and Resistance Metrics^{9, 15-17}

• Tracking antimicrobial use (AU) is required by the Centers for Medicare and Medicaid Services in the United States. The CDC’s National Healthcare Safety Network (NHSN) Antimicrobial Use and Resistance (AUR) module is the route by which facilities report and analyze antimicrobial use and resistance data to meet this requirement. 

• Days of therapy (DOT) became the preferred metric for antibiotic use even before the requirement to submit data to NHSN.  AU is reported to NHSN as antimicrobial days per 1,000 days present. Antimicrobial days are determined using electronic or bar code antibiotic administration data and are defined as any amount of a specific agent administered in a calendar day to a patient regardless of the number of doses. Days present is determined by aggregating the number of patients in a patient care location or facility anytime throughout a day during a calendar month.  

• The Standardized Antimicrobial Administration Ratio or SAAR is a risk-adjusted measure created by the CDC calculated by dividing the observed antimicrobial use (reported by the facility) by the predicted antimicrobial use (calculated using predictive models). The SAAR can be used to track use, compare to national benchmarks, and analyze impact of interventions. Facilities need to consider patient specific factors when determining ideal targets as the SAAR does not include any assessment of appropriateness of therapy. 

• Other Antibiotic Use Metrics

• Defined daily dose (DDD) may be useful in resource limited settings or when there is no access to electronic medication administration data. DDD was the first standardized measure of antibiotic use and was developed by the World Health Organization. DDD is determined using the average dose per day for a medication used for its main indication in adults and does not always correspond to the recommended dose prescribed. 

• Length of therapy (LOT) is the number of days of antimicrobial therapy regardless of the number of agents used. LOT can be used to describe duration for an individual admission and can be used to evaluate interventions designed to optimize duration of therapy.

• Antimicrobial resistance (AR) 

• AR data can be used to monitor infection prevention and AMS efforts. Submitting AR data to the CDC NHSN module is one mechanism for meeting this need. The AR option of the module reports resistance information as a proportion with the proportion susceptible determined by using the number of susceptible isolates divided by the total number of isolates tested.

• The Standardized Resistant Infection Ratio or SRIR was created by the CDC for facilities to evaluate their rates of hospital-onset drug-resistant infections compared to national benchmarks. The ratio is determined by taking the number of observed resistant infections that meet NHSN resistance definitions divided by the number of predicted resistant infections. The latter is determined by adjusting for risk factors that have been associated with resistant infections.  A Pathogen-Specific Standardized Infection Ratio (pSIR) is also available to allow for benchmarking rates of hospital-onset infections of specific pathogens to a national benchmark. Facilities that submit data to NHSN can also receive a facility-wide antibiogram table displaying percent susceptibilities.  This antibiogram will only include data for the organisms and antibiotic susceptibilities reported to NHSN which may not include all those isolated at a particular facility. 

• Developing and distributing cumulative antibiograms is another way programs can consider monitoring antibiotic resistance data. More information about antibiograms is available here. 

Financial Metrics^3-4,6-7,9-11

• Demonstrating cost savings was one of the primary metrics used to justify early AMS programs. Documenting financial impact can be useful in establishing return on investment and obtaining necessary resources, and programs should consider monitoring antibiotic costs and hospital costs.  

• Cost alone should not be the primary metric determining program effectiveness as factors such as patent expiration, drug shortages, prevalence of resistant organisms necessitating more expensive agents, and others are outside the purview of AMS programs. After an initial decrease in costs, stabilization will likely occur and a shift toward cost containment will be necessary.  Removal of support for AMS programs has been associated with increased costs.

• Antibiotic costs

• Since purchasing data is typically available from hospital pharmacy departments, measurement of direct antibiotic expenditures is an easy way for AMS programs to track antibiotic costs. Many factors impact antibiotic costs (inflation, shortages, contracts, etc.), and costs vary between facilities and countries making benchmarking challenging.  

• Measuring costs based on prescriptions or antibiotic administrations normalized for patient census may be more valuable and allow for comparisons between institutions.  Antibiotic cost per patient day or antibiotic cost per admission are examples of this strategy. 

• Recognizing that some AMS interventions may increase cost, when for example a more expensive agent is the best choice for treating a certain patient or infection, it is necessary to balance cost savings with effectiveness and patient safety. 

• Hospital costs

• AMS program interventions may impact costs related to length of stay, emergency department visits, intensive care days, readmissions, and laboratory testing resources.  Tracking these outcomes either individually or using total hospital cost per admission can encourage facility leaders to continue supporting AMS efforts.  

• Measuring cost avoidance is more challenging.  Efforts to quantify costs saved from prevention of adverse effects, C. difficile infection, and readmission are difficult. 

Regulatory Requirements for Metrics in the United States^12-13

• Several accreditation organizations have standards for Antimicrobial Stewardship including the Joint Commission and DNV.  The Joint Commission standards require that organizations monitor antibiotic use by analyzing DOT or by reporting this data to NHSN. They require programs to evaluate adherence to at least one facility-specific evidence-based guideline and to collect, analyze, and report data on resistance patterns, prescribing practices, or AMS activities to hospital leadership and prescribers. 

• The Centers for Medicare and Medicaid Services Promoting Interoperability Program requires submission of antibiotic use and antibiotic resistance data to NSHN effective calendar year 2024 for eligible hospitals and critical access hospitals.

Future Metrics^4,9,14

• Antibiotic use data which incorporates patient-level information would provide facilities with better information for purposes of benchmarking. 

• Collecting and analyzing antibiotic use data by spectrum of activity would allow comparison between regimens. For example, vancomycin/piperacillin-tazobactam versus nafcillin/metronidazole both have the same DOT but a very different spectrum of activity.

• Syndrome based metrics that utilize the electronic medical record to improve efficiencies in data collection through automation, natural language processing, or standardization of data.  Artificial  intelligence (AI) could be used to gather information from the electronic health record, identify predictors of antibiotic use for specific patient and facility types, and analyze adherence to metrics. The use of AI might be advantageous as it could eliminate the need for manual chart review. However, these tools need to be trained and potential biases need to be resolved. 

• Metrics for quality and tied to performance are expected to expand in the United States due to efforts for transparency in reimbursement. 

References:

1. Fishman N. Policy Statement on Antimicrobial Stewardship by the Society for Healthcare Epidemiology of America (SHEA), the Infectious Diseases Society of America (IDSA), and the Pediatric Infectious Diseases Society (PIDS). Infection Control & Hospital Epidemiology. 2012;33(4):322-327. doi:10.1086/665010 

2. Barlam TF, Cosgrove SE, Abbo LM, et al.  Implementing an antibiotic stewardship program: guidelines by the Infectious Diseases Society of America and the Society for Healthcare Epidemiology of America. Clin Infect Dis. 2016;62(10):e51-e77. https://pubmed.ncbi.nlm.nih.gov/27080992/

3. CDC. Core Elements of Hospital Antibiotic Stewardship Programs. Atlanta, GA: US Department of Health and Human Services, CDC; 2019. Available at https://www.cdc.gov/antibiotic-use/core-elements/hospital.html

4. Moehring R, Vaughn V. Development of inpatient stewardship metrics: is it time for public reporting? Infect Dis Clin N Am. 2023;37:853-871. https://pubmed.ncbi.nlm.nih.gov/37661471/

5. World Health Organization. Antimicrobial stewardship programmes in health-care facilities in low-and middle-income countries: a WHO practical toolkit. Available at: https://www.who.int/publications/i/item/9789241515481. Accessed January 25, 2024.

6. O’Riordan F, Shiely F, Byrne S, Fleming A. Quality indicators for hospital antimicrobial stewardship programmes: a systematic review. J Antimicrob Chemother. 2021;76(6):1406-1419. https://pubmed.ncbi.nlm.nih.gov/33787876/

7. National Quality Forum. National Quality Partners Playbook: Antibiotic Stewardship in Acute Care. Available at: https://www.qualityforum.org/Publications/2016/05/Antibiotic_Stewardship_in_Acute_Care_Playbook.aspx. Accessed January 19, 2024.

8. Centers for Disease Control and Prevention. Core Elements of Hospital Antibiotic Stewardship Programs. Atlanta, GA: US Department of Health and Human Services, CDC; 2019. Available at https://www.cdc.gov/antibiotic-use/core-elements/hospital.html.

9. Al-Hasan MN, Winders HR, Bookstaver PB, Justo JA. Direct measurement of performance: a new era in antimicrobial stewardship. Antibiotics (Basel). 2019;8(3):127. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6784134/

10. Bennett N, Schulz L, Boys S. Newland JG. Understanding inpatient antimicrobial stewardship metrics. Am J Health Syst Pharm. 2018;75:23-238. https://pubmed.ncbi.nlm.nih.gov/29436469/

11. Morris AM. Antimicrobial stewardship programs:  appropriate measures and metrics to study their impact. Curr Treat Options Infect Dis. 2014;6:101-112. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4431704/

12. Centers for Disease Control and Prevention. FAQs: AUR reporting for the CMS Promoting Interoperability Program.  Available at: https://www.cdc.gov/nhsn/cms/cms-faq-aur.html. Accessed January 19, 2024.

13. The Joint Commission.  New and revised requirements for antibiotic stewardship. Available from: https://www.jointcommission.org/standards/r3-report/r3-report-issue-35-new-and-revised-requirements-for-antibiotic-stewardship/ Accessed February 2, 2023.

14. Ilges D, Tande AJ, Stevens RW. A broad spectrum of possibilities: spectrum scores as a unifying metric of antibiotic utilization. Clin Infect Dis. 2023;77:167-173. https://pubmed.ncbi.nlm.nih.gov/36999909/

15. National Healthcare Safety Network. Antimicrobial use and resistance (AUR) module. Available at: https://www.cdc.gov/nhsn/psc/aur/index.html. Accessed January 5, 2024.

16. Centers for Disease Control and Prevention. Antimicrobial use and resistance (AUR) module reports. Available at: https://www.cdc.gov/nhsn/datastat/aur-reports.html. Accessed February 6, 2024.

17. Yarrington ME, Moehring RW. Basic, advanced, and novel metrics to guide antibiotic use assessments. Curr Treat Options Infect Dis. 2019;11(145-160). https://doi.org/10.1007/s40506-019-00188-3