Impact of modified microbiology reporting on the treatment of low-risk AmpC Enterobacterales infections: a multi-centre controlled interrupted time series study

OBJECTIVES: We assessed the impact of a modified microbiology report and cascade that selectively reported narrower-spectrum β-lactams for low-risk AmpC Enterobacterales (AmpC-E). METHODS: We conducted a controlled interrupted time series analysis to assess the proportion of patients receiving ceftriaxone or piperacillin/tazobactam on the fourth day of antibiotic treatment for low-risk AmpC-E infection (Serratia marcescens, Morganella morganii, Providencia spp., Citrobacter koseri) compared with a high-risk AmpC-E (Enterobacter cloacae complex, Klebsiella aerogenes, Citrobacter freundii) control group. Secondary outcomes included a pre-post measurement of antibiotic use on the fourth day of therapy, death at 30 days, and recurrent infection at 90 days. RESULTS: Patients with low-risk AmpC-E infections were more likely to receive ceftriaxone or piperacillin/tazobactam compared with high-risk AmpC-E controls [incidence rate ratio (IRR) 39.8, 95% CI 1.8-871.7, P = 0.02]. There was an upward shift and trend in ceftriaxone and piperacillin/tazobactam use during the implementation period in the low-risk AmpC-E group compared with the control group (IRR 3.3, 95% CI 0.9-11.9, P = 0.07 and slope 1.3, 95% CI 1.0-1.8, P = 0.10), with an associated reduction in fluoroquinolone use. During the implementation period, 30 day mortality (13.8% versus 12.1%, P = 0.70) and recurrent infection at 90 days (6.4% versus 5.7%, P = 0.83) were similar between low-risk and high-risk AmpC-E groups. CONCLUSIONS: Modification of microbiology reporting for low-risk AmpC Enterobacterales infections to selectively report narrower-spectrum β-lactams resulted in a rapid and sustained increase in use of ceftriaxone and piperacillin/tazobactam across two hospitals. Aligning this microbiology reporting with guidelines would have scalable impact on hospital antimicrobial stewardship.