Hiroyuki Suzuki, Abhishek Pandya, Shinya Hasegawa, Joseph Tholany

Although guidelines recommend adjunctive rifampin and gentamicin use for patients with staphylococcal prosthetic valve endocarditis (PVE), evidence behind the recommendation is limited and conflicting. We performed a retrospective cohort study of all patients with staphylococcal PVE within the Veterans Health Administration during 2003-2021. Patients were identified with diagnostic codes for prosthetic valves and positive blood cultures for Staphylococcus species and confirmed via manual chart reviews. The primary outcome was the composite of all-cause mortality or recurrence of staphylococcal PVE within one year from diagnosis. Inverse probability of treatment weighting (IPTW) was used to estimate the probability of individuals receiving rifampin using propensity scores. IPTW-adjusted multivariable Cox regression analysis was used to compare outcomes between patients who received rifampin and gentamicin, and those did not. Among 373 patients with staphylococcal PVE, 275 (73.7%) and 225 (60.3%) received at least one dose of rifampin and gentamicin, respectively. The incidence of staphylococcal PVE increased from 0.47 (2003-11) to 0.77 (2012-21) per 10,000 hospitalizations. Gentamicin use declined over time (70.1% in 2003-2011 to 54.8% in 2012-2021, p = 0.04) while rifampin use did not change significantly (76.1% in 2003-2011 to 72.4% in 2012-2021, p = 0.43). The composite outcome was observed in 209 (56.0%). Neither rifampin use (adjusted hazard ratio [HR] 0.77, 95% CI 0.48-1.24) and gentamicin use (adjusted HR 1.11, 95% CI 0.71-1.74) was associated with the composite outcome. No significant association was observed between adjunctive rifampin or gentamicin use and improved outcomes.