Platelet dynamics in methicillin-susceptible and methicillin-resistant Staphylococcus aureus bacteremia: Distinct...

To characterize platelet dynamics in Staphylococcus aureus bacteremia (SAB) by methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains and determine their association with clinical outcomes.

Single-center retrospective study including all SAB episodes between 2006 and 2022. Platelet counts were recorded at baseline, days 3, and 7 and stratified by quartiles. Primary outcome was 30-day mortality, and secondary outcome persistent bacteremia. A multivariable logistic regression model estimated adjusted mortality risk based on day 3 platelet quartiles.

A total of 1609 SAB episodes were included (1242 MSSA; 367 MRSA). Mortality was inversely associated with platelet count with an adjusted odds ratio (aOR) 3.11 (95% confidence interval 1.74-5.59) for Q1 (platelets ≤114 × 10³/µL), 2.02 (1.10-3.69) for Q2 (114-180 × 10³/µL), and 1.57 (0.85-2.92) for Q3 (180-270 × 10³/µL) vs Q4 (>270 × 10³/µL) in MSSA bacteremia, independent of septic shock. In MRSA, only Q1 (<116 × 10³/µL) was significantly associated with increased mortality (aOR 3.09, 1.16-8.20). Low platelet count (≤150 × 10³/µL) at day 3 was also associated with persistent bacteremia in MSSA (24.8% vs 17.4%, P = 0.002) and MRSA episodes (32.8% vs 22.3%, P = 0.033).

Platelet count showed an inverse dose-response association with mortality and bacteremia persistence, particularly, in MSSA. These findings highlight the value of platelet dynamics in SAB management.