Emergency Department Ultrasonographic Probe Contamination and Experimental Model of Probe Disinfection

Abstract

We evaluate the frequency of emergency department (ED) ultrasonographic probe contamination and the bacterial species involved and evaluate probe cleaning and disinfection methods. This was a 3-part observational cross-sectional study. Surveillance cultures were taken of linear and curvilinear probes on 3 ultrasonographic machines between patient encounters. Cultures of uncovered probes were taken immediately after scanning of skin and soft tissue infections. After experimental probe contamination with methicillin-resistant Staphylococcus aureus (MRSA), we assessed 3-step disinfection by sequential cleaning with a dry towel, saline solution-moistened towel, and quaternary ammonia germicidal wipe and 1-step disinfection by germicidal wipe alone. Cultures were obtained by applying the probe to a blood agar plate. In part 1, of 164 surveillance cultures obtained from 6 probes on 29 sampling days during 11 months, 111 (67%; 95% confidence interval [CI] 60% to 74%) grew normal skin flora or environmental flora, 52 had no growth (32%; 95% CI 25% to 39%), and 2 (1.2%; 95% CI 0.3% to 4.3%) grew a clinically important pathogen. In part 2, 14 of 20 (70%; 95% CI 48% to 85%) cultures taken after skin and soft tissue infection scanning produced heavy growth of a clinically important pathogen, including 13 S aureus (5 MRSA). In part 3, cleaning with a dry and moist towel reduced but did not eliminate MRSA. The germicidal wipe step resulted in no growth in 15 of 15 (100%; 95% CI 80% to 100%) cultures in 3-step disinfection and in 9 of 10 (90%; 95% CI 60% to 98%) when used alone. Skin and environmental flora are commonly present on ultrasonographic probes between patient encounters in our ED; however, clinically important pathogens are uncommon. S aureus (including MRSA) frequently contaminates uncovered probes during skin and soft tissue infection scanning, but in an experimental model, MRSA appears to be reliably removed by a quaternary ammonia germicidal wipe if the probe is partially cleaned first.