Stethoscopes used in an intensive care unit (ICU) are loaded with bacteria, including those that may be associated with hospital-acquired infections (HAIs), new data show. Moreover, standard cleaning methods did not eliminate the problems.

“Practitioner stethoscopes are contaminated by a plethora of bacteria, including organisms that may be associated with nosocomial infections. Cleaning reduces contamination but does not bring the bacterial biomass down to the level of clean stethoscopes nor does it significantly change the overall community composition. Thus, stethoscopes are a potential vector of HAI transfer,” the researchers write.

The study by Vincent R. Knecht, BS, from the Division of Pulmonary, Allergy and Critical Care, Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, and colleagues was published online December 12 in Infection Control and Hospital Epidemiology.

“It is well documented that practitioner stethoscopes are not routinely disinfected, and studies based on bacterial culture show that they may be contaminated with potential pathogens including methicillin-resistant and
-sensitive Staphylococcus spp, multidrug-resistant P. aeruginosa, Acinetobacter spp, Enterococcus spp, Escherichia coli, Klebsiella spp, and Streptococcus spp…. Culture-based studies are limited, however, because culture can only identify agents of a priori interest but not entire microbial communities that may be present,” the researchers explain.

Therefore, the researchers used bacterial 16S ribosomal RNA gene sequencing to gain “unbiased profiling of entire bacterial communities” present on stethoscopes used in a medical ICU.

In the first set of stethoscopes (set A), they tested 20 stethoscopes carried by practitioners (physicians, nurses, and respiratory therapists), 20 individual-use patient-room stethoscopes, and 20 clean unused individual-use stethoscopes. In a second set (set B), the researchers tested 10 practitioner stethoscopes that were sampled before and after standardized cleaning (wiping vigorously with a hydrogen peroxide wipe for 60 seconds and left to dry).

Set C contained an additional 20 practitioner stethoscopes that were sampled before and after cleaning by the practitioner using the practitioner’s usual method of cleaning. Practitioners used hydrogen peroxide wipes (n = 14), alcohol swabs (70% isopropyl alcohol; n = 3), or bleach wipes (n = 3) to clean their stethoscopes and followed their personal preference regarding duration of cleaning.

The researchers found that all stethoscopes used in the ICU were significantly contaminated with a variety of pathogens. The highest bacterial contamination levels were found on practitioner stethoscopes, followed by patient-room stethoscopes. Bacterial contamination levels on clean stethoscopes and background controls were indistinguishable from each other.

Table. Potential Nosocomial Pathogens on Practitioner Stethoscopes

Staphylococcus spp were present on all stethoscopes; the investigators were able to determine the species on some of those, and more than half were contaminated with Staphylococcus aureus, even after practitioner cleaning.

“Both cleaning methods resulted in a significant reduction in bacterial contamination regardless of cleaning method,” the authors write. “In the standardized cleaning group, 5 of 10 stethoscopes fell below the level of the clean stethoscopes…. In the practitioner-preferred cleaning group, 2 of 10 stethoscopes fell below the level of clean stethoscopes.”

“This study underscores the importance of adhering to rigorous infection control procedures, including fully adhering to CDC [Centers for Disease Control and Prevention]–recommended decontamination procedures between patients, or using single-patient-use stethoscopes kept in each patient’s room,” senior author Ronald Collman, MD, a professor of medicine and pulmonary, allergy and critical care at the University of Pennsylvania Perelman School of Medicine, Philadelphia, said in a news release.