Absence of patient-to-patient intrahospital transmission of Staphylococcus aureus as determined by whole-genome sequencing.
Bottom Line: To identify patient-to-patient intrahospital transmission using high-resolution genetic analysis, we sequenced the genomes of a consecutive set of 398 S. aureus isolates from sterile-site infections.The S. aureus strains were collected from four hospitals in the Houston Methodist Hospital System over a 6-month period.In addition, our data demonstrate that highly related pools of S. aureus strains exist in the community which may complicate outbreak investigations.
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Mentions: In our study of invasive S. aureus disease across a multihospital system, we could identify no closely related isolates with an obvious intrahospital transmission path. In addition, there was no significant clustering of isolates based on the hospital of origin (Fig. 6). We discovered some isolate pairs that were closely related genetically yet lacked an obvious transmission chain. Many of these isolate pairs consisted of patients with infections already present on admission to the hospital. Subsequently, our results suggest that there are clonal pools of S. aureus present within the community that result in patients being infected with closely related organisms prior to their admission to the hospital. This result concurs with observations made recently by Prosperi et al. (29). Thus, it may not be unusual for two patients to be admitted to the same hospital with highly related strains, but conventional typing methods would not differentiate between this and a scenario in which patient-to-patient transmission had occurred. This situation has been previously suggested (31) and underscores the need not only to document infections present at admission but to use tools that provide the necessary resolution to distinguish the two. One potential limitation is that we chose to study only sterile-site infections. Any transmission involving nonsterile sites such as superficial skin or wounds would have been missed in our study.