Staphylococcus aureus infections; Lead by the nose

An overview and the latest insights regarding S. aureus nasal carriage, associated risks of developing infections and possible preventive measures, will be given in Chapter 2. Since mupirocin efficacy studies in preventing nosocomial infections have only been performed in surgical and dialysis patients, we decided to design and perform a mupirocin efficacy study in non-surgical patients. These patients are also responsible for a great burden in S. aureus hospital infections. This randomized, placebo-controlled trial is described in Chapter 3. This trial lead to four new research questions: 1. What is the risk of nosocomial S. aureus bacteremia for S. aureus carriers versus noncarriers? 2. Is there a difference in risk of mortality for carriers versus non-carriers once bacteremic with S. aureus? 3. What is the efficacy of mupirocin on reducing S. aureus carriage at extra-nasal sites? 4. Can invasive S. aureus strains be identified by genotyping? The first two research questions are addressed in Chapter 4. Chapter 5 describes a study in which the effect of mupirocin on nasal, pharyngeal and perineal carriage of S. aureus is investigated (question 3). Chapter 6 describes a nested-case control study where genotyping data of invasive S. aureus strains are compared to non-invasive strains (question 4). Development of prophylactic strategies are always based on the understanding of the pathogenesis of the specific disease. The mechanisms underlying S. aureus nasal carriage and how nasal carriage results in disease are still incompletely understood. We decided to study whether nose picking is a determinant of S. aureus nasal carriage. Nose picking behaviour seems to be an obvious determinant, but was never studied before. In collaboration with the department of otolaryngology, we performed a study on nose picking behaviour and S. aureus nasal carriage, which we describe in Chapter 7. When we study S. aureus, we can extrapolate these findings to methicillin resistant S. aureus (MRSA). This is essentially the same micro-organism, the only difference is that the latter is more difficult to treat with antibiotics. The Netherlands are well known for their low prevalence rate of MRSA in the hospitals. In the U.S.A. more than 40% of the S. aureus strains cultured from hospitalized patients are methicillin-resistant, as compared to less than 1% in the Netherlands. In the Netherlands, MRSA could usually be related to a hospital admission in a foreign country, indicating that most MRSA strains were imported into the country. But in the last few years there were reports that many MRSA strains could not be related to sources abroad. Therefore, we wanted to know the prevalence of MRSA carriage in patients admitted to the hospital with no relation to a foreign admission. We performed such a prevalence study with an improved detection technique, as described in Chapter 8 and Chapter 9. All studies included in this thesis are based on the assumption that the anterior nares are the main reservoir for S. aureus in humans. All studies, their results and conclusions are, therefore, "lead by the nose".