Staphylococcus aureus and endocarditis

The bacterium Staphylococcus aureus can cause a wide spectrum of disease. Bloodstream infection (S. aureus bacteraemia, SAB) is a serious form of S. aureus infection, potentially leading to spread of the infection to distant sites via the bloodstream. Once in the bloodstream, S. aureus can also attach itself to the valves of the heart, causing infective endocarditis (IE). IE is one of the most feared complications of SAB because of its ability to destroy cardiac tissues such as heart valves and because of the propensity for embolic complications such as cerebral stroke. In this thesis, we explore how to better identify the patients with SAB who have IE or other complications. After a general introduction (chapter 1), we describe the clinical and epidemiological profile of SAB in a multicenter cohort of 7 hospitals in the Netherlands (chapter 2) and describe which patient and disease factors pose the most risk for serious complications of the disease (chapter 3). In chapter 4, we demonstrate that clinical criteria can identify SAB patients with a very low risk of IE. Furthermore, we examine the impact of so-called immortal time bias on the effect of performance of a radiological test ([18F]FDG-PET/CT) on mortality in patients with SAB (chapter 5). Next, we turn to endocarditis in general, and examine the prognostic effect follow-up blood cultures in patients with IE not caused by staphylococci (chapter 6). Finally, we examine the diagnostic impact of searching for immunological phenomena in patients with suspected IE (chapter 7) and evaluate the new Duke-ISCVID diagnostic criteria for IE (chapter 8). Chapter 9 places the findings of the thesis into perspective and discusses the implications for future care and research.