Extended-spectrum beta-lactamase (ESBL) screening swabs are performed widely as a means of identifying ESBL carriers and preventing transmission. We tested whether these results could have unintended benefits in predicting the ESBL status of subsequent infections with E. coli and Klebsiella spp. experienced by these patients.
A retrospective cohort study was conducted using an auto-populated antimicrobial stewardship database. Patients were included if 18 years of age or older, admitted to hospital between 2010 and 2015, and screened for ESBL prior to developing an E. coli or Klebsiella spp. sterile-site infection Test characteristics were derived using the screening swab ESBL result as test variable predicting the presence or absence of ESBL in the sterile site Enterobacteriaceae species.
2254 patients had sterile cultures positive for E. coli or Klebsiella spp. during the study period, and a total of 73/2254 patients had prior screening for ESBL (3%). Within this sample population a total of 27/73 screening swabs were positive for ESBL (37%), and a total of 28/73 sterile cultures were positive for ESBL (38%). The overall specificity of ESBL swabs was 89% (75%-96%) and the overall sensitivity was 79% (59%-91%). The positive predictive value was 81% (61%-93%) and the negative predictive value was 87% (73%-95%). The positive likelihood ratio was 7 (3-17) and the negative likelihood ratio was 0.24 (0.12-0.49). In the United States, where the prevalence of ESBL among Enterobacteriaceae sterile isolates is as high as 0.23, a positive ESBL screening swab would yield a post-test probability of 0.68 of third-generation cephalosporin resistance and a negative swab would yield a post-test probability of 0.067 (based on the derived likelihood ratios).
Prior ESBL screening swab results are a useful tool for predicting ESBL status of sterile site E. coli and Klebsiella spp. infections. The results of this study suggest that those with a positive ESBL screening swab should receive empiric carbapenem therapy for positive E. coli and Klebsiella spp. sterile cultures. Patients with negative ESBL screening swabs that are not critically ill may be treated with a carbapenem-sparing empiric regimen while awaiting sensitivity results.
D. Macfadden, None
N. Daneman, None