December 26, 2013
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Patient transmission causes minority of ICU S. aureus acquisitions

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Data from whole-genome sequencing suggest that few Staphylococcus aureus acquisitions in the ICU are the result of patient-to-patient transmission.

“Before the introduction of enhanced hand-hygiene and universal antiseptic use, patient-to-patient transmission of S. aureus may have been more common,” the researchers wrote in Clinical Infectious Diseases. “Our findings do not undermine the importance of current infection control practices; rather they support their efficacy.”

The researchers, from the Brighton and Sussex Medical School at the University of Sussex in England, evaluated patient-to-patient transmission of S. aureus in an adult ICU from 2010 to Feb. 28, 2011. Patients were screened for S. aureus carriage within 24 hours of admission. Of the 1,181 patient-stays, 185 patients had S. aureus. There were 680 patients who had two or more samples taken during their stay to assess for S. aureus carriage, and there were 44 acquisitions in 41 patients.

S. aureus was cultured from 329 samples and 275 isolates underwent spa-typing. There were three spa-types associated with 67.6% of all methicillin-resistant S. aureus isolates. But for methicillin-sensitive S. aureus, only two spa-types comprised more than 5% of the total. Among the 44 acquisitions, seven isolates could not undergo typing. Of the remaining 37, five met the criteria for patient-to-patient transmission based on overlapping stay with another patient who had the same spa-type. All were MRSA patients.

When the five instances of patient-to-patient transmission underwent whole-genome sequencing, the researchers found that only two of the cases were actual patient-to-patient transmission, but the remaining three acquisitions were genetically distinct from potential sources and from each other. However, whole-genome sequencing also identified five additional transmissions, although patients had not shared time on the ICU and had different spa-types.

“[Our findings] indicate that whole-genome sequencing can be used to assess the efficacy of infection control measures to prevent S. aureus transmission,” they wrote. “Studies to evaluate other nosocomial sources of S. aureus (eg, the environment, health care workers, visitors, the food chain) are challenging. Health care workers and hospital managers are anxious about identifying staff as potential sources of S. aureus. Nevertheless, our findings demonstrate that such studies are required and emphasize the value of whole-genome sequencing.”

Disclosure: The researchers report no relevant disclosures.