Thrombocytopenia in Staphylococcus aureus bacteremia: risk factors and prognostic importance

Mayo Clin Proc. 2011 May;86(5):389-96. doi: 10.4065/mcp.2010.0705.


Objective: To identify risk factors and outcomes associated with thrombocytopenia at sepsis onset in Staphylococcus aureus bacteremia.

Patients and methods: This single-center, retrospective, cohort study consists of all adult patients with a first episode of clinical S aureus bacteremia between April 1, 1988, and September 30, 1994, and between January 1, 1999, and December 31, 2007. Thrombocytopenia was defined as a platelet count less than 150 × 10(9)/L. The primary outcome was 30-day all-cause mortality. Risk factors for 30-day all-cause mortality were identified using univariate and multivariable analyses. Multivariable analysis was conducted using forward step logistic regression analysis. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for risk of death.

Results: A total of 1052 patients had clinical S aureus bacteremia. Thrombocytopenia at sepsis onset was present in 235 patients (22.3%). Thrombocytopenia was associated with community-acquired bacteremia, infections caused by methicillin-sensitive S aureus, high-magnitude bacteremia (defined as >4 positive blood cultures [≥ 3 separate positive blood culture sets]), and endocarditis. Patients with thrombocytopenia presented more commonly with severe sepsis reflected by septic shock and acute renal failure. Thirty-day mortality was significantly higher among patients with thrombocytopenia (132/235 [56.2%]) vs those without thrombocytopenia (281/817 [34.4%]; P<.001). Higher mortality was associated with the degree of thrombocytopenia. In multivariable analysis, thrombocytopenia at baseline remained an independent risk factor for 30-day mortality (OR, 2.82; 95% CI, 1.87-4.24). The adjusted association between thrombocytopenia and death remained similar among the 917 patients with monomicrobial bacteremia (OR, 2.88; 95% CI, 1.83-4.53) and the 945 patients who did not die within the first 48 hours (OR, 2.88; 95% CI, 1.87-4.45.).

Conclusion: We observed a strong association between thrombocytopenia at sepsis onset and all-cause mortality in S aureus bacteremia, possibly related to mechanisms other than sepsis alone.

MeSH terms

  • Aged
  • Area Under Curve
  • Bacteremia / complications*
  • Bacteremia / mortality*
  • Cause of Death
  • Chi-Square Distribution
  • Female
  • Humans
  • Logistic Models
  • Male
  • Platelet Count
  • Prognosis
  • ROC Curve
  • Retrospective Studies
  • Risk Factors
  • Staphylococcal Infections / complications*
  • Staphylococcal Infections / mortality*
  • Staphylococcus aureus
  • Thrombocytopenia / complications*
  • Thrombocytopenia / mortality*