Consequences of Excluding Enterococcus faecium as a Typical Endocarditis Pathogen in the Duke-ISCVID Criteria: Endocarditis Is Endocarditis Even if the Bacterium Is Uncommon

To the Editor—The 2023 Duke-ISCVID (International Society for Cardiovascular Infectious Diseases) criteria, recently published in your journal, provide many new important aspects to the diagnostic criteria for infective endocarditis (IE) [1]. The revised criteria keep the original format of the Duke criteria, including major imaging and major microbiology criteria, complemented with minor criteria [1–3]. Whereas methods for imaging have been revolutionized since the introduction of the Duke criteria in 1994 [2], the microbiological methods have developed but are still, in essence, the same. The more sophisticated imaging techniques have likely led to radically increased sensitivity and specificity as compared with the 1990s, whereas the sensitivity of the microbiological method remains high and the specificity remains low. This development should, in our opinion, result in a more pronounced emphasis on the imaging modalities in the diagnostic criteria for IE.

One of the changes in the 2023 Duke-ISCVID criteria is that Enterococcus faecium is no longer considered a “typical endocarditis pathogen” and thus 2 positive blood cultures with E. faecium are regarded as a minor criterion [1, 3]. In the previous version, non-nosocomial E. faecium bacteremia with unknown focus was considered as a typical endocarditis pathogen [3]. It is generally accepted that IE is rare in bacteremia with E. faecium [4, 5]. However, E. faecium can indeed cause IE and the consequence of the reclassification of the species is shown in Figure 1 with data from the Swedish Registry for Infective Endocarditis (SRIE) [6].

Figure 1.

Consequence of the Dukes-ISCVID 2023 reclassification of E.faecium on IE, data from the Swedish Registry for Infective Endocarditis 2008–2023. Abbreviations: IE, infective endocarditis; ISCVID, International Society for Cardiovascular Infectious Diseases.

There were 7679 cases of patients treated for IE reported to the SRIE between 2008 and the present. Of these, 52 episodes (0.7%) were caused by E. faecium. Figure 1 demonstrates the consequences for the classification of these 52 cases by the proposed changes of the criteria. Importantly, in the 14 cases reclassified from definite IE to possible IE with the Duke-ISCVID criteria, 13 patients had vegetations demonstrated with echocardiography in conjunction with positive blood cultures with E. faecium. In 1 case, a patient with pacemaker vegetations was reclassified from possible to definite IE with the Duke-ISCVID criteria since pacemaker has been added as a minor criterion in the latter [1].

The sensitivity of the ISCVID-Duke criteria thus decreases when E. faecium is excluded from the “typical endocarditis pathogens.” The Duke-ISCVID criteria chose to include nosocomially acquired Enterococcus faecalis bacteremia with known focus as a major criterion, although IE is known to be rare in this condition [7]. The argument for including E. faecalis was that the sensitivity of the criteria increased [8].

Our observations on E. faecium endocarditis point to the fact that it does not matter if a bacterium is a common or a rare cause of IE when the patient has IE as determined by echocardiography and concomitant bacteremia. We propose that the diagnostic criteria for IE could be revised so that patients fulfilling major imaging criteria and having significant bacteremia, irrespective of species, should be regarded as definite IE. In cases with negative imaging, the propensity of the bacterium to cause IE should be considered as well as other minor criteria.

Notes

Financial support. M. R. reports grants or contracts unrelated to this work from Swedish Governmental Funds for Clinical Research. There was no funding for this study.