Survival time of Staphylococcus aureus on ultrasound probes

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The use of ultrasound (US) transducer heads on patient skin requires the use of a coupling gel. If not properly cleaned between patients the risk for cross contamination increases, potentially leading to healthcare associated infections (HAIs). This study examined survival time of Staphylococcus aureus (SA) in various matrices” Levine et al (2019).

Abstract:

BACKGROUND: The use of ultrasound (US) transducer heads on patient skin requires the use of a coupling gel. If not properly cleaned between patients the risk for cross contamination increases, potentially leading to healthcare associated infections (HAIs). This study examined survival time of Staphylococcus aureus (SA) in various matrices.

METHODS: Nine US heads were sterilized and clamped with heads level. Overnight cultures of SA were diluted in sterile saline or tryptic soy broth (TSB). Aliquots of the diluted culture were placed on the US heads in various matrices including US gel, and dried using low-pressure filtered air. The US heads were incubated for three days at room temperature. Surviving SA was removed from US heads at 1, 24, and 72 hours using sterile transport swabs. Viable SA was quantified on tropic soy agar following incubation at 37°C for 24 hours. Calculations of percent survival of SA were made for the six different inorganic and organic matrices tested. Statistical comparison of the data was made using a factorial ANOVA (time by matrix) with post -hoc analysis.

RESULTS: Survival of SA on the US heads varied by time and matrix in which the cells were mixed. Over 80% of SA placed on US heads survived for 1 hour, with survival found for up to three days based on the organic matrices the cells were dried in. The one hour SA survival in US gel and full-strength TSB was significantly greater than all other matrices (p < .01). When SA was mixed into different concentrations of TSB survival was variable (3.0%-8.6%). CONCLUSIONS: The survival of SA on US heads suggests a need for improved cleaning/disinfecting of US heads. Further research is warranted to investigate cleaning protocols, disinfection solutions, and other options to reduce the threat of HAIs from US heads.

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Reference:

Levine, D., Spratt, H., McDonald, S.S. and Noonan, K. (2019) Survival Time of Staphylococcus aureus on Ultrasound Heads. American Journal of Infection Control. 47(6), p.S17. DOI: https://doi.org/10.1016/j.ajic.2019.04.019.

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