What Is the Significance of <b><i>Staphylococcus aureus </i></b>Colonization in Hemodialysis Patients?

studies, however, reported on the frequency of extra-nasal S. aureus colonization in the absence of nasal colonization. In the current issue of Nephron , Eells et al. investigated this question by simultaneously obtaining cultures from 100 hemodialysis patients from 3 body sites (nares, oropharynx, and inguinal) [6] . They observed S. aureus colonization in 42% of patients, including 36% with methicillin sensitive S. aureus (MSSA) and 6% with MRSA. These frequencies of S. aureus colonization are in line with those reported from other dialysis centers ( table 1 ). The authors further noted that 10% of patients had colonization only in the nares, but not at the other two locations. Conversely, 14% of patients had colonization only at one or more extra-nasal locations, but not in the nares. In other words, one-third of patients (14/42) with documented S. aureus colonization would have been missed had the investigators obtained only nasal cultures. Importantly, genetic analysis of the 20 patients with S. aureus cultured from more than one site established that these contemporaneous cultures were from an identical strain, in agreement with previous studies suggesting clonality [5, 7] . There has been an ongoing interest in understanding the nature of the relationship between S. aureus colonization and systemic infection, the role of screening for colonization, and whether eradication of colonization in asymptomatic patients can prevent systemic infections. MRSA colonization in hemodialysis patients has been associated with a higher subsequent risk of infection and bacteremia [8] and a 2.46-fold higher risk of all-cause Infection is the second leading cause of hospitalization and mortality among hemodialysis patients after cardiovascular disease [1] . Staphylococcus aureus (S. aureus) infections are extremely common in the hemodialysis population, and their incidence is 100-fold greater in the hemodialysis population than that observed in the general population [1] . These infections often result in major medical complications, prolonged hospital stays, and high economic costs [2] . The relationship between S. aureus colonization and infection remains a subject of ongoing debate. Numerous studies from around the world have documented a high prevalence of S. aureus colonization in hemodialysis (HD) patients ( table 1 ), at a rate, which far exceeds that observed in the general population [1] . Factors contributing to this high rate of colonization include the patients’ immunocompromised state, as well as their frequent hospitalizations and surgeries. The hemodialysis population is particularly susceptible to colonization with MRSA as a consequence of the frequent administration of antimicrobial agents, as well as regular exposure to health care systems [1] . Most published studies on S. aureus colonization in hemodialysis patients have obtained only nasal cultures ( table 1 ), with the implicit assumption that nasal colonization is a representative of the colonization at other locations. The majority of these studies did not obtain cultures from other sites to confirm this hypothesis. Three studies documented extra-nasal S. aureus colonization in 32–40% of patients with nasal colonization [3–5] . None of these Received: December 10, 2014 Accepted after revision: December 18, 2014 Published online: February 13, 2015