Infective endocarditis caused by non-HACEK Gram-negative bacteria, a registry-based comparative study

Introduction/objectives
Infective endocarditis (IE) caused by non-HACEK Gram-negative bacteria (nHGNB) is uncommon. In the 2023 Duke-ISCVID diagnostic criteria, Pseudomonas aeruginosa and Serratia marcescens were added as “typical” pathogens. We examine the consequences of this addition, the risk of IE in bacteremia from nHGNB species and the features of IE caused by nHGNB.

Materials and methods
nHGNB IE cases reported to the Swedish Registry of Infective Endocarditis (SRIE) 2008-2023 were identified. Episodes of bacteremia caused by nHGNB during the same period in Region Skåne were used as controls. Characteristics of IE caused by nHGNB were compared with those of other pathogens reported to the SRIE.

Results
114 episodes of nHGNB IE, of which 98 (87%) were definitive, were identified (1.5% of all cases). Escherichia coli was the most common cause (28%) followed by Pseudomonas aeruginosa (13%) and Klebsiella (9%). Applying the Duke-ISCVID criteria, none of the possible IE episodes caused by P. aeruginosa or S. marcescens were reclassified to definitive IE. Comparing the proportion of the nHGNB species in episodes with IE to episodes with bacteraemia (n=33213), E. coli was more common in bacteraemia than in IE whereas P. aeruginosa and Serratia were more common in IE. Patients with nHGNB IE frequently had underlying diseases and the mortality was higher than in streptococcal IE.

Discussion
Our findings indicate that P. aeruginosa and Serratia are more common in IE than in bacteremia but that that their status as “typical IE-pathogens” in the Duke-ISCVID criteria did not improve the performance of the criteria.