Diagnostic prediction tools for bacteraemia caused by 3rd generation cephalosporin-resistant Enterobacteriaceae in suspected bacterial infections: a nested case-control study

Objectives Current guidelines for empirical antibiotic treatment poorly predict the presence of 3rd generation cephalosporin resistant Enterobacteriaceae (3GC-R EB) as a cause of infection, thereby increasing unnecessary carbapenem use. We aimed to develop diagnostic scoring systems to better predict the presence of 3GC-R EB as a cause of bacteraemia. Methods A retrospective nested case-control study was performed that included patients ≥18 years in whom blood cultures were obtained and intravenous antibiotics were initiated. Each patient with 3GC-R EB bacteraemia was matched to four control infection episodes within the same hospital, based on blood culture date and onset location (community or hospital). Starting from 32 described clinical risk factors at infection onset, selection strategies were used to derive scoring systems for the probability of community- and hospital-onset 3GC-R EB bacteraemia. Results 3GC-R EB bacteraemia occurred in 90 of 22,506 (0.4%) community-onset and in 82 of 8,110 (1.0%) hospital-onset infections, and these cases were matched to 360 community-onset and 328 hospital-onset control episodes, respectively. The derived community-onset and hospital-onset scoring system consisted of 6 and 9 predictors, respectively, with c-statistics of 0.807 (95% confidence interval 0.756-0.855) and 0.842 (0.794-0.887). With selected score cutoffs, the models identified 3GC-R EB bacteraemia with equal sensitivity as existing guidelines, but reduced the proportion of patients classified as at risk for 3GC-R EB bacteraemia (i.e. eligible for empiric carbapenem therapy) with 40% in patients with community-onset and 49% in patients with hospital-onset infection. Conclusions These prediction rules for 3GC-R EB bacteraemia may reduce unnecessary empiric carbapenem use.