Implementation of a Multimodal Diagnostic Algorithm for Blood Culture-Negative Infective Endocarditis at the Argentine National Reference Laboratory: A Prospective Study

Background: Blood culture-negative infective endocarditis (BCNIE) poses a significant diagnostic challenge. This study evaluated a multimodal diagnostic algorithm combining serological and molecular methods at the Argentine National Reference Laboratory. Methods: A prospective analysis was conducted on 53 consecutive patients with suspected BCNIE referred between January 2019 and December 2024. The diagnostic workflow included indirect immunofluorescence for Bartonella spp. and Coxiella burnetii, species-specific PCR for Bartonella spp. and Tropheryma whipplei, and broad-range 16S rRNA PCR with Sanger sequencing on available blood and valvular tissue specimens. Results: An etiological diagnosis was established in 17 of 53 patients (32.1%). Bartonella spp. was the predominant pathogen (47.1%; 8/17), followed by T. whipplei (35.3%; 6/17) and Streptococcus spp. (17.6%; 3/17). All Bartonella cases were initially detected via serology, with molecular confirmation achieved exclusively through valvular tissue analysis. Conclusions: Implementing a standardized multimodal diagnostic algorithm significantly enhances etiological yields in BCNIE. The findings emphasize the complementary value of frontline serology and targeted molecular testing, highlighting that simultaneous submission of serum, blood, and valvular tissue is essential for optimal diagnosis.