1016. Denominator Matters in estimating Antimicrobial Use: A comparison of days present and patient days
Session: Poster Abstract Session: Antibiotic Stewardship: General Acute Care Implementation and Outcomes
Friday, October 28, 2016
Room: Poster Hall
  • Moehring Denominators IDW16 final.pdf (337.3 kB)
  • Background: A new method for antimicrobial use (AU) rate denominator calculations, termed days present, has been introduced in the NHSN’s AU Option. This study aims to compare patient days and days present to a “gold standard” of person-time to determine implications of the choice of denominator on days of therapy-based AU rate estimates.

    Methods: We performed a post-hoc analysis of room level, bed flow data including date-time of entry and exit at 5 community hospitals and 2 academic medical centers that participated in the Benefits of Terminal Room Disinfection Study from April 2012 to July 2014. Person time in days was calculated by subtracting date-time of room exit from date-time of room entry. Patient days were counted by the midnight census method. Unit-level days present were counted if the patient was on an inpatient unit for any portion of a calendar day. Facility-level counts for days present did not double count calendar days when patients transferred between units during the same hospital stay. Percent relative differences (RD) on the facility and unit level for patient days and days present were compared to person time among hospitals and units.

    Results: Over 1.7 million days of person time were evaluated among the 7 hospitals and 125 units over the 28-month period. Person time lengths of stay were median 2.8 days (IQR 1.7-5.6) per hospital stay and 2.1 days (IQR 1.1-4.0) per unit stay. Patient days were close underestimates of person time [median RD -0.66 % (-1.50 to -0.08) among hospitals]. Days present calculations included median 29% excess days compared to person time and varied among hospitals (IQR 17 to 30%). RDs among stays on general medical/surgical units were median 28% (IQR 26-29%) higher. Higher RDs were also seen in unit types with short stays and lower AU (e.g. cardiology 54%, labor and delivery 48%) compared to unit types with long stays (e.g. bone marrow transplant 9%, burn unit 8%).

    Conclusion: Relative differences of days present to person time were influenced by short stays. The presence of excess days in aggregated days present may lower AU estimates in facilities and units that care for patients with short stays. Stewards transitioning from patient days to days present denominators should be aware of these differences.

    Rebekah W. Moehring, MD, MPH1,2,3,4, Yuliya Lokhnygina, MS, PhD5, Elizabeth Dodds Ashley, PharmD, MHS, FCCP, BCPS1,6, Arthur W. Baker, MD, MPH7, Sarah S. Lewis, MD MPH4, Daniel Sexton, MD1 and Deverick Anderson, MD, MPH, FIDSA, FSHEA1,4, (1)Duke Antimicrobial Stewardship Outreach Network, Durham, NC, (2)Duke Infection Control Outreach Network (DICON), Durham, NC, (3)Durham VA Medical Center, Durham, NC, (4)Division of Infectious Diseases, Duke University Medical Center, Durham, NC, (5)Biostatistics and Bioinformatics, Duke University, Durham, NC, (6)Duke Antimicrobial Stewardship Outreach Network (DASON), Durham, NC, (7)Duke Infection Control Outreach Network, Durham, NC


    R. W. Moehring, None

    Y. Lokhnygina, None

    E. Dodds Ashley, None

    A. W. Baker, None

    S. S. Lewis, None

    D. Sexton, None

    D. Anderson, None

    Findings in the abstracts are embargoed until 12:01 a.m. CDT, Wednesday Oct. 26th with the exception of research findings presented at the IDWeek press conferences.