Eligibility of patients with Staphylococcus aureus bacteraemia for early oral switch

To identify people with low-risk Staphylococcus aureus bacteraemia (SAB), the SABATO investigators screened 5063 people, finding 213 (4·2%) meeting their eligibility criteria1. This low proportion of eligible patients led the authors to question if low-risk SAB is clinically relevant. We aimed to determine the clinical relevance of the SABATO definition of low-risk SAB, and if the trial population was representative of potentially eligible real-world patients. Data was collected retrospectively for 464 consecutive adults with SAB at our institution (Supplementary Figure), approved by the South East Scotland Research Ethics Committee (23/SS/0025). We then applied the SABATO inclusion and exclusion criteria to identify potentially eligible real-world patients.

Of the 464 patients in our cohort, 71 (15·3%) would have been potentially eligible for inclusion in the trial. Acquisition of SAB in these patients was mainly nosocomial (35/71, 49·3%). Key cohort characteristics reported by the trial were very similar when comparing trial participants with potentially eligible real-world patients, although the median Charlson Comorbidity Index was lower in the trial cohort (Table). An intravenous catheter was the most common source of SAB in both cohorts, but there was a higher proportion of SAB from an unknown source in the real-world group (p=0·0015). An unknown source is a risk factor for complications2,3 and further evaluation combined with intensive follow-up of early oral switch should be considered in this group.

Implanted prosthetic material is a component of the IDSA definition of complicated SAB4 but with certain caveats was not an absolute exclusion criterion in the SABATO trial. Nine potentially eligible real-world patients had prosthetic material in situ (n=4 cardiac devices and n=5 orthopaedic implants). This data was not reported for trial participants but could further increase confidence in applicability of the findings. No laboratory or physiology data from the time of the index blood culture was reported but might have been helpful to quantify disease severity and guide patient selection (Supplementary Table). We suggest this supports standardised collection and reporting of cohort characteristics in SAB trials to improve comparability between studies, which is often complicated by variability in the cohort characteristics reported5.

We conclude that the sub-group of low-risk SAB studied in the SABATO trial is clinically relevant and find the similarities between randomised and real-world eligible patients re-assuring. Implementation of SABATO findings should be done cautiously and studied prospectively, especially when applied to patients with SAB of unknown source who were infrequently included in the trial.