Antimicrobial Usage and Outcomes following Laboratory Suppression of Antimicrobial Susceptibility Results for Pseudomonas aeruginosa in Sputum Cultures

Background:

Pseudomonas aeruginosa isolates from sputum cultures do not always require treatment, often representing chronic airways colonization. By releasing sputum P. aeruginosa antimicrobial susceptibility results, only after specific phone request by treating doctors, we aimed to reduce use of ciprofloxacin without compromising clinical outcomes.

Methods:

From 26 February 2015, antimicrobial susceptibility results for P. aeruginosa in sputum were routinely suppressed except for immunosuppressed, Intensive Care Unit, cystic fibrosis or bronchiectasis patients. A database search of the Wollongong Hospital Microbiology laboratory information system identified 108 patients with susceptibility results suppressed (26 Feb 2015 - 25 Feb 2017), compared with 108 patients where antimicrobial susceptibility results were routinely reported (26 Feb 2013 - 25 Feb 2015). Data collected included age, sex, residency, admission date and diagnosis, comorbidities, allergy, empirical and definitive antibiotic treatment, date of sputum culture, resistance patterns of P. aeruginosa, ciprofloxacin usage, Antimicrobial Stewardship interventions, length of stay, inpatient mortality and readmission within 30 days.

Results:

The prevalence of P. aeruginosa in sputum cultures was 11% (1252/11388). Patient characteristics were comparable in the two groups. Ciprofloxacin use was significantly reduced post-intervention [26.9% (29/108) versus 39.8% (43/108); p= 0.043] as well as Guidance MS approvals [9.03% (87/963) versus 17.72% (188/1061); p=0.000001].  Interrupted time series analysis of this intervention was not associated with a significant change in the rates of ciprofloxacin use.

Rates of ciprofloxacin resistance were lower post-intervention [2.8% (3/108) versus 16.7% (18/108); p= 0.0006], reaffirmed by SQL database search of the OMNI-Client [9.30% (32/343) versus 15.00% (60/399); p= 0.0187].

 

Ciprofloxacin usage against resistance over time

 

There was no difference in length of stay, 30-day readmission and mortality.

Conclusion:

This study offers a successful model of collaboration between the microbiology laboratory and antimicrobial stewardship activity. It showed a reduction in use of ciprofloxacin with possible influence on P. aeruginosa resistance rates, without affecting patient outcomes.