Low-Dose Acetylsalicylic Acid Treatment and Impact on Short-Term Mortality in Staphylococcus aureus Bloodstream Infection: A Propensity Score-Matched Cohort Study.

Objectives: Staphylococcus aureus bloodstream infection is associated with considerable mortality. Experimental models suggest a direct antistaphylococcal effect of acetylsalicylic acid, but evidence from human studies is scarce. We aimed to estimate the effect of low-dose acetylsalicylic acid therapy on mortality in bloodstream infections caused by S. aureus compared with Escherichia coli.

Design: Retrospective cohort study based on observational data from 838 and 602 episodes of S. aureus and E. coli bloodstream infection, respectively.

Setting: Swiss tertiary referral center.

Patients: Adult patients with S. aureus and E. coli bloodstream infection, respectively, categorized according to low-dose acetylsalicylic acid therapy as outpatient or inpatient before bacteremia.

Interventions: None.

Measurements And Main Results: Thirty-day all-cause mortality was analyzed in a total of 314 propensity score-matched S. aureus bloodstream infection and in 268 E. coli bloodstream infection patients, respectively (1:1 match of low-dose acetylsalicylic acid users and nonusers). S. aureus bloodstream infection cases and controls were equally matched for relevant confounders except treatment with statins, which was strongly associated with a low-dose acetylsalicylic acid use (p < 0.001). At day 30, 12.1% of cases and 27.4% of controls had died (hazard ratio, 0.40; p < 0.001). Low-dose acetylsalicylic acid use was associated with a reduced 30-day all-cause mortality in multivariate analysis (hazard ratio, 0.38; 95% CI, 0.21-0.69; p = 0.001) of matched patients and also of the entire cohort (n = 689) after adjustment for the propensity score (hazard ratio, 0.58, 95% CI, 0.34-0.98; p = 0.04). In contrast, low-dose acetylsalicylic acid use was not associated with the primary endpoint in patients with E. coli bloodstream infection (hazard ratio, 0.78; 95% CI, 0.40-1.55; p = 0.8).

Conclusions: Low-dose acetylsalicylic acid at the time of bloodstream infection was strongly associated with a reduced short-term mortality in patients with S. aureus bloodstream infection. Future studies are required to investigate if early low-dose acetylsalicylic acid is a suitable treatment in patients with S. aureus bloodstream infection.