Thrombocytopaenia during methicillin-sensitive Staphylococcus aureus bacteraemia

The prognostic impact of thrombocytopaenia in Staphylococcus aureus bacteraemia (SAB) has previously been determined at bacteraemia onset only and relevant pre-bacteraemic thrombocytopaenia predisposing parameters have not been accounted for. We evaluated the prognostic impact of low thrombocyte count in SAB excluding pre-bacteraemic factors potentially causing thrombocytopaenia. This was a multicentre retrospective analysis of methicillin-sensitive SAB (MS-SAB) patients. Thrombocyte count was determined at blood culture collection and at days 3 and 7. Thrombocytopaenia was defined as a thrombocyte count less than 150 ×10⁹/L. Patients with chronic alcoholism, liver diseases and haematologic malignancies were excluded. Altogether, 495 patients were identified. Thrombocytopaenia at blood culture and at day 3 associated to endocarditis (p < 0.05 and p < 0.01) and defervescence (p < 0.001 and p < 0.01). Mortality at 90 days was higher for patients with thrombocytopaenia at blood culture collection (26 vs. 16%, p < 0.05), at day 3 (32 vs. 13%, p < 0.01) and at day 7 (50 vs. 14%, p < 0.001). In receiver operating characteristic analyses, thrombocytopaenia predicted a poor outcome at blood culture collection (p < 0.05), at day 3 (p < 0.001) and at day 7 (p < 0.001). When accounting for all prognostic parameters, thrombocytopaenia at day 3 [hazard ratio (HR), 1.83; p = 0.05] demonstrated a trend towards poor outcome, whereas thrombocytopaenia at day 7 (HR, 3.64; p < 0.001) associated to poor outcome. Thrombocytopaenia at blood culture collection was not a prognostic parameter when all prognostic factors were taken into account. However, thrombocytopaenia at day 3 indicated a poor outcome and thrombocytopaenia at day 7 was a significant independent negative prognostic marker that has not been previously reported in SAB.