Staphylococcal Enterotoxin P Predicts Bacteremia in Hospitalized Patients Colonized With Methicillin-Resistant Staphylococcus aureus

(See the editorial commentary by Stevenson and Wang on pages 488–90.) Staphylococcus aureus is a major cause of healthcare-associated infections [1], and patients are often colonized with this bacterium before developing invasive disease [2, 3]. Increasing carriage of methicillin-resistant S. aureus (MRSA), an antibiotic-resistant strain, has resulted in a doubling of MRSA-related hospitalizations, including up to 56 000 US hospitalizations per year for MRSA bacteremia [4–6]. Overall, nearly 19 000 patients die annually in US hospitals from MRSA infections [7]. MRSA carriage in the United States is at least 7% in general hospital populations [8] and as high as 24% in intensive care units (ICUs) [9]. The risk of MRSA infection in the year following colonization is as high as 33%, with 18% being primary bloodstream infections [10]. Nasal carriers of MRSA versus methicillin-susceptible S. aureus (MSSA) have a 4 times higher incidence of bacteremia, with >80% of cases involving an identical strain in the nares and the blood [3, 11, 12]. In addition, the mortality for bacteremia is 2 times higher with MRSA as compared to MSSA [13]. Both host and pathogen factors play a role in the development of MRSA infections. Host factors include prolonged hospitalization [14–17], advanced age [10, 14], intravenous catheterization [15, 17–19], mechanical ventilation [18, 20, 21], antibiotic exposure [17, 21], soft-tissue wounds [15, 19], and chronic diseases, such as diabetes, renal insufficiency, cancer, and malnutrition [10, 18, 22]. Pathogen factors predicting MRSA bacteremia are the subject of ongoing debate [23]. Studies accounting for epidemiologic factors of the host in addition to genetic variation in different MRSA strains are lacking. We therefore sought to look at combined host and pathogen factors in a prospective cohort.