Distribution of Causative Organisms in Infective Endocarditis and Their Associated Mortality Risk: A Single-Centre Study From North Wales, United Kingdom

Background Infective endocarditis (IE) is a life-threatening infection of the endocardial surface, most commonly affecting native or prosthetic valves and intracardiac devices. Despite advancements in diagnosis and treatment, IE continues to carry a high mortality risk. Blood cultures remain a cornerstone of diagnosis, typically yielding positive results and enabling identification of the causative organisms. <i>Staphylococcus aureus</i> is now recognised as the most prevalent pathogen, particularly in healthcare-associated and intravenous drug use-related cases, and is associated with worse outcomes. Other commonly implicated organisms include streptococci and enterococci. This study aimed to investigate the distribution of causative pathogens and their associated mortality risk in patients diagnosed with IE at the Wrexham Maelor Hospital, North Wales, United Kingdom. Method A retrospective cohort study was conducted using patient data from the Welsh Clinical Portal at the Wrexham Maelor Hospital, covering the period from June 2022 to May 2025. Patients were eligible for inclusion if they had a confirmed diagnosis of IE based on the modified Duke criteria. Statistical analysis was performed using Chi-squared or Fisher's exact test to evaluate associations between pathogen type and mortality. Results A total of 50 patients with positive blood cultures were included. <i>Staphylococcus aureus</i> was the most frequently isolated organism (n=19; 38%), followed by polymicrobial infections (n=7; 14%), <i>Staphylococcus epidermidis</i> (n=4; 8%), and <i>Enterococcus faecalis</i> (n=3; 6%). <i>Streptococcus sanguinis</i>, <i>Escherichia coli</i>, and <i>Haemophilus parainfluenzae</i> each accounted for 4% (n=2), with the remaining 2% (n=1) comprising less common pathogens. Twenty-three deaths were recorded, with the highest mortality observed in the culture-negative group (n=6). No statistically significant correlation was found between the pathogen type and mortality. Conclusion While <i>Staphylococcus aureus</i> was the most frequently isolated pathogen, the highest mortality occurred in patients with culture-negative IE. This may reflect the diagnostic and therapeutic challenges posed by the absence of microbiological confirmation, potentially delaying appropriate, targeted antimicrobial therapy. These findings highlight the importance of early diagnosis, empiric antimicrobial coverage, and timely treatment adjustments to improve outcomes in IE, particularly in culture-negative presentations.