Prevalence and Risk Factors for Non-HACEK Gram-negative Bacillus Endocarditis: A Retrospective Analysis

Infective endocarditis (IE) caused by non-HACEK gram-negative bacilli (GNB) is challenging to diagnose and is associated with high morbidity and mortality. There is growing literature highlighting the differences in IE prevalence amongst various GNB; therefore, there is an impetus to characterize these traditionally "atypical" organisms to accurately risk stratify this complex infectious diagnosis.

This investigation was a retrospective cohort study conducted at 2 health care institutions in the USA. All hospitalized adult patients with bloodstream infection with a prespecified GNB (Enterobacter cloacae, Escherichia coli, Klebsiella aerogenes, Klebsiella pneumoniae, Klebsiella oxytoca, Pseudomonas aeruginosa, and Serratia marcescens) between January 1, 2018 to December 31, 2022, were included. Chart review was performed to collect clinical information, IE risk factors, and diagnosis of IE.

Among 6678 patients with GNB bacteremia, 82 (1.2%) developed IE. The prevalence of IE among patients with Serratia marcescens or Pseudomonas aeruginosa bacteremia was higher than that with Enterobacteriaceae, with increased risk amongst patients with a history of injection drug use (43.1% vs 9.3%) and prosthetic valves (19.5% vs 2.2%). There was no statistically significant species variation in IE prevalence when endocardial device was present. Importantly, we found discordance in clinical practice in the use of diagnostic echocardiography in patients with a high risk of GNB IE.

Serratia marcescens and Pseudomonas aeruginosa have a higher prevalence of IE compared with Enterobacteriaceae, with the differential risk most pronounced among patients with a history of injection drug use and prosthetic valves. This highlights the opportunity to optimize the diagnosis of IE amongst patients with GNB bacteremia.