Stratification of cumulative antibiograms in hospitals for hospital unit, specimen type, isolate sequence and duration of hospital stay.
BACKGROUND
Empirical antibiotic therapy is based on patients' characteristics and antimicrobial susceptibility data. Hospital-wide cumulative antibiograms may not sufficiently support informed decision-making for optimal treatment of hospitalized patients.


METHODS
We studied different approaches to analysing antimicrobial susceptibility rates (SRs) of all diagnostic bacterial isolates collected from patients hospitalized between July 2005 and June 2007 at the University Hospital in Zurich, Switzerland. We compared stratification for unit-specific, specimen type-specific (blood, urinary, respiratory versus all specimens) and isolate sequence-specific (first, follow-up versus all isolates) data with hospital-wide cumulative antibiograms, and studied changes of mean SR during the course of hospitalization.


RESULTS
A total of 16 281 isolates (7965 first, 1201 follow-up and 7115 repeat isolates) were tested. We found relevant differences in SRs across different hospital departments. Mean SRs of Escherichia coli to ciprofloxacin ranged between 64.5% and 95.1% in various departments, and mean SRs of Pseudomonas aeruginosa to imipenem and meropenem ranged from 54.2% to 100% and 80.4% to 100%, respectively. Compared with hospital cumulative antibiograms, lower SRs were observed in intensive care unit specimens, follow-up isolates and isolates causing nosocomial infections (except for Staphylococcus aureus). Decreasing SRs were observed in first isolates of coagulase-negative staphylococci with increasing interval between hospital admission and specimen collection. Isolates from different anatomical sites showed variations in SRs.


CONCLUSIONS
We recommend the reporting of unit-specific rather than hospital-wide cumulative antibiograms. Decreasing antimicrobial susceptibility during hospitalization and variations in SRs in isolates from different anatomical sites should be taken into account when selecting empirical antibiotic treatment.
Kuster
Stefan P
SP
Division of Infectious Diseases and Hospital Epidemiology, University Hospital, Zurich, Switzerland.
Ruef
Christian
C
Zbinden
Reinhard
R
Gottschalk
Jochen
J
Ledergerber
Bruno
B
Neuber
Lutz
L
Weber
Rainer
R
D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001419:Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D003428:Cross Infection / Q000188:drug therapy / Q000382:microbiology; D016905:Gram-Negative Bacterial Infections / Q000188:drug therapy / Q000382:microbiology*; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy / Q000382:microbiology*; D006785:Hospitals, University; D006801:Humans; D008826:Microbial Sensitivity Tests; D013557:Switzerland
D000900:Anti-Bacterial Agents