Can ultrasound probes and coupling gel be a source of nosocomial infection in patients undergoing sonography? An in vivo and in vitro study.

OBJECTIVE: At our institution, ultrasound probes are wiped with a clean, dry, soft, absorbent paper towel after each procedure as a basic standard of probe disinfection. However, it was unclear if this provided a sufficient level of decontamination. This study was designed to determine if the ultrasound probe and coupling gel can act as a vector of nosocomial infection and to describe a cost-effective method of probe handling that allows optimal control of infection. SUBJECTS AND METHODS: In the first part of the study, the ultrasound probe was exposed to the disrupted skin of patients recruited from our inpatient population, using our routine scanning technique to look for subcutaneous collections. Twenty-seven patients were scanned: 17 with surgical wounds, seven with surgical drains, four with enteric stomas, three with biopsy sites, and three with ulcers or excoriation. Fifteen patients had a discharge associated with their disrupted skin, and seven patients had culture-proved skin infections. Each probe was wiped with a clean, dry paper towel after scanning, then immersed in a brain-heart infusion (BHI) broth, and the solution was cultured. In the second part of the study, the ultrasound probe was exposed to a large inoculum of bacteria. Sixty-one probes were used to scan fields of confluent growth of bacteria on agar plates. Twenty-six probes were cleaned by wiping with a dry, clean paper towel, and 25 probes were cleaned by wiping with a dry, clean paper towel followed by immersion in Hibidil (0.05% chlorhexidine weight/volume). Ten probes functioned as controls and were not cleaned after exposure to the bacteria. Each probe was then immersed in BHI broth, and the solution was cultured. In the third part of the study, the coupling gel was evaluated as a culture medium for bacterial growth. Twenty-five agar plates were inoculated with a confluent growth of bacteria. Half of the surface of each agar plate was covered with coupling gel, and the remaining surface was left unexposed. The resulting bacterial growth on each side of the plates was compared.
RESULTS: One of the 27 probes exposed to patients with disrupted skin grew Staphylococcus epidermidis (skin flora). For probes exposed to a large inoculum of bacteria, we found no statistically significant difference in the number of probes that showed bacterial growth on culture between probes cleaned by wiping with a towel and those cleaned with Hibidil. Furthermore, the resulting bacterial growth in both sets of probes was scant and was not considered clinically significant. All 10 control probes showed clinically significant growth in all cases. As for evaluation of the coupling gel as a culture medium, the gel permitted bacterial growth and did not show any evidence of bacteriocidal or bacteriostatic properties.
CONCLUSION: Ultrasound probes that are wiped with a paper towel until they are visibly clean do not contribute to nosocomial infections. Additional antiseptic solutions such as Hibidil are not necessary. We suggest that probes be simply wiped with a clean, dry, nonsterile paper towel between procedures, including probes used on contaminated scanning fields, open wounds, and cutaneous infections. After the final procedure of the day, probes should be cleaned with a liquid cleaning solution such as Hibidil to remove all traces of coupling gel, which could support the overnight growth of bacteria. This would decontaminate the probes and prevent the overnight growth of bacteria. This method would be both a cost-effective and time-efficient protocol for controlling infection.