Materials and methods

Study design and setting

This retrospective observational study was conducted at Royal Derby Hospital, a UK teaching DGH providing secondary and tertiary cardiology services. Consecutive adult patients who underwent TOE for suspected IE between April 2022 and October 2024 were identified from the departmental echocardiography database. Clinical records, microbiology results, imaging studies, operative reports, and electronic medical records were reviewed retrospectively. The diagnosis of IE was established using the modified Duke criteria in conjunction with multidisciplinary clinical assessment, microbiological findings, and echocardiographic evidence, in accordance with contemporary international guidelines [1,7].

Study population

A total of 145 consecutive TOE examinations performed for suspected IE were screened. Examinations relating to cases in which IE was not confirmed and duplicate or repeat examinations relating to the same infective episode were excluded. The final study cohort consisted of 133 unique confirmed clinical episodes of IE.

Patients aged 18 years or older with confirmed IE who underwent TOE during the study period were eligible for inclusion. No cases classified as possible IE were included in the final cohort. Repeat TOE examinations performed during the same infective episode were considered part of a single clinical episode and were not analysed separately.

As this was a retrospective observational study that included all consecutive eligible patients during the study period, no formal a priori sample size calculation was performed.

Data collection

Patient demographics, cardiovascular risk factors, predisposing cardiac conditions, microbiological results, echocardiographic findings, treatment strategies, and clinical outcomes were extracted from electronic health records. Data extraction was performed using the hospital electronic medical record system and departmental echocardiography database. Where discrepancies were identified, the records were reviewed manually to ensure data accuracy.

The variables collected were age; sex; pre-existing valvular heart disease; prosthetic heart valves; CIEDs; a history of previous IE; blood culture results; causative microorganisms; the affected cardiac valve or intracardiac structure; the presence of vegetations; peri-annular abscess formation; prosthetic valve involvement; device-related infection; the requirement for cardiac surgery or device extraction; and in-hospital mortality.

Echocardiographic assessment

All TOE examinations were performed according to departmental protocols by experienced consultant cardiologists with expertise in TOE and IE.

The recorded TOE findings included vegetation location and size, valve involvement, leaflet perforation, abscess formation, prosthetic valve infection, paravalvular complications, and evidence of CIED infection.

Dental exposure and antibiotic prophylaxis

Dental history was obtained from the electronic medical records and, where patients were alive and contactable, through direct telephone contact. Patients without documented dental exposure in the available records or patient history were classified as having no documented dental exposure. Dental exposure was defined as documentation of an invasive dental procedure involving manipulation of the gingival tissues or periapical region of the teeth or perforation of the oral mucosa within the six months preceding the diagnosis of IE.

Documentation of antibiotic prophylaxis before dental procedures was also recorded where available. Causative microorganisms were classified as oral flora organisms if blood cultures yielded viridans group streptococci, anginosus group streptococci, Streptococcus pneumoniae, Enterococcus faecalis, or Streptococcus gallolyticus/S. bovis. E. faecalis and S. gallolyticus/S. bovis were included because of their documented oral carriage, although both also colonise the gastrointestinal tract.

Study outcomes

The primary outcome was the association between documented recent dental procedures and oral flora-associated IE.

The secondary outcomes included the microbiological profile, echocardiographic characteristics, distribution of native- and prosthetic-valve infections, requirement for cardiac surgery or device extraction, in-hospital mortality, and documentation of antibiotic prophylaxis before dental procedures.

Statistical analysis

Continuous variables are presented as the mean ± SD or median with IQR, depending on the data distribution. Categorical variables are expressed as frequencies and percentages.

Comparisons between categorical variables were performed using the chi-square test or Fisher’s exact test, as appropriate. Continuous variables were compared using Student’s t-test or the Mann-Whitney U test, according to the data distribution.

ORs with 95% CIs were calculated to evaluate the association between documented dental exposure and oral flora-associated IE. Statistical significance was defined as a two-sided p-value of <0.05. Statistical analyses were performed using IBM SPSS Statistics, version 30 (IBM Corp., Armonk, NY, USA). Given the relatively small number of oral flora-associated IE cases (n = 44), multivariable logistic regression was not performed because the inclusion of multiple covariates could have resulted in overfitting and unstable estimates. The primary association was therefore assessed using an unadjusted odds ratio with a 95% CI.

Ethical considerations

This study was conducted as a retrospective observational service evaluation using routinely collected clinical data. All patient information was anonymised before analysis in accordance with institutional information governance policies. Ethical approval and individual informed consent were waived in accordance with local governance requirements for retrospective service evaluations.