Can Stethoscopes Transmit Multidrug-Resistant Bacterial Pathogens?

With burdens of nosocomial infections steadily on the rise, it is important to determine sources of direct contact transmission.

The diaphragm of a stethoscope has been regarded as the second-most contaminated area, after the fingertips, but stethoscopes have not been studied in depth as a vector of nosocomial infection. Although few studies have explored the link between stethoscopes and bacterial infection transmission, most of the findings have been limited to Staphylococcus.

But now, investigators from the College of Medicine at the Catholic University of Korea in Seoul, South Korea, have conducted a prospective observational study to determine whether stethoscopes are a potential carrier of nosocomial multidrug-resistant bacteria. The findings of their research were presented today in a poster presentation at the Society for Healthcare Epidemiology of America Spring Conference (SHEA 2019).

The investigation was conducted as a part of a quasi-experimental study in a 450-bed hospital in South Korea. A total of 89 doctors and nurses agreed to participate and, of those individuals, 86 stethoscopes were sampled. The investigators imprinted the diaphragm of the instruments for 6-10 seconds on blood agar plates. For each sample, bacterial loads were calculated by total colony-forming units (CFU) and the potential nosocomial pathogens were identified. In total 85 of the 86 stethoscopes (98.8%) were contaminated with a mean CFU of 27.91 ± 32.46.

According to the investigators, 20 of the 85 contaminated stethoscopes (23.5%) were confirmed to have at least 1 potential pathogen, with Staphylococcus aureus detected in 13 of the 20 instances. Other detected isolates include Enterococcus, Enterobacter, and Klebsiella, Methicillin-resistant S aureus, and extended-spectrum beta-lactamase-producing Klebsiella pneumoniae.

Yet, no isolates of vancomycin-resistant Enterococcus, carbapenemase-producing Enterobacteriaceae, MDR-Acinetobacter, nor Pseudomonas were detected in this study.

The health workers were also surveyed via questionnaire about their cleaning procedures. Survey results indicate that 58 of the 89 participants (65.2%) were female and 44 (49.4%) were doctors.

Only 19 of the 89 participants (21.3%) reported cleaning their stethoscopes regularly at least 1 time a day. The investigators observed that physicians were less likely to clean their stethoscopes (gender adjusted; p = 0.001; odds ratio [OR], 12.750; 95% confidence interval [CI], 2.730-59.546), and were more likely to use their own stethoscopes instead of using the stethoscopes that were designated for examining isolated patients infected with MDR pathogens (gender adjusted; p<0.001; OR, 8.762; CI, 2.911-26.373).

However, the investigators note “there were no significant risk factors associated with the contamination rate and bacterial load when multivariate regression analysis performed using variables such as gender, job, age group, department, cleaning method, and frequency of stethoscope cleaning.”

Although the study determined that the majority of stethoscopes were contaminated, and contamination by nosocomial pathogens was 23.5%, MDR pathogens were only detected in a small proportion. And although physicians were less likely to clean their personal stethoscopes or use designated stethoscopes to prevent against infection in this study, there were no significant risk factors associated with contamination of the tool.

Based on this research, the investigators concluded that there is a need for an evidence-based disinfection manual for stethoscopes.

The study, “Stethoscope as A Potential Carrier of Multi-Drug Resistant Bacterial Pathogens?; Preliminary Data of Quasi-Experimental Study,” was presented on April 24, 2019, at SHEA in Boston, Massachusetts.