ICU Stethoscopes Foster DNA from Nosocomial Bacteria

A molecular analysis of bacterial contamination on stethoscopes in an intensive care unit conducted by Vincent R. Knecht and his colleagues at University of Pennsylvania Perelman School of Medicine, Philadelphia, has shown that stethoscopes used in an ICU carry bacterial DNA reflecting complex microbial communities that include nosocomially important taxa. Commonly used cleaning practices reduce contamination but are only partially successful at modifying or eliminating these communities.

Stethoscopes are often used on multiple patients and have been considered as vectors for hospital-based bacterial contamination. Culture-based studies from past literature, which focus on individual organisms, have implicated stethoscopes as potential vectors of nosocomial bacterial transmission. However, the full bacterial communities that contaminate in-use stethoscopes have not been investigated. To determine this, the investigators used bacterial 16S rRNA gene deep-sequencing, analysis, and quantification to profile entire bacterial populations on stethoscopes in use in an intensive care unit (ICU), including practitioner stethoscopes, individual-use patient-room stethoscopes, and clean unused individual-use stethoscopes. Two additional sets of practitioner stethoscopes were sampled before and after cleaning using standardized or practitioner-preferred methods. Thus, the authors used molecular methods to investigate the bacterial status of stethoscopes used in medical ICUs, even those that are used only once, and whether conventional methods of cleaning stethoscopes effectively decontaminate them and, if not, what microbes may be found on them.

The findings reflected that bacterial contamination levels were highest on practitioner stethoscopes, followed by patient-room stethoscopes, whereas clean stethoscopes were indistinguishable from background controls. Bacterial communities on stethoscopes were complex, and community analysis by weighted UniFrac showed that physician and patient-room stethoscopes were indistinguishable and significantly different from clean stethoscopes and background controls. Genera relevant to healthcare-associated infections (HAIs) were common on practitioner stethoscopes, among which Staphylococcus was ubiquitous and had the highest relative abundance (6.8%–14% of contaminating bacterial sequences). Other HAI-related genera were also widespread although lower in abundance. The investigators found evidence of colonies of the following bacteria linked to hospital-associated infections on stethoscopes carried by healthcare professionals in the ICU:  Staphylococcus (including S. aureus), Pseudomonas, Acinetobacter, Clostridium, Enterococcus, Stenotrophomonas, and Burkholderia. Cleaning the stethoscopes using a number of recommended methods had only a modest effect on removing the amount of bacteria detected in this manner on stethoscopes. There was a significant reduction in bacterial contamination levels, but these levels reached those of clean stethoscopes in only a few cases with either standardized or practitioner-preferred methods, and bacterial community composition did not significantly change.

“This study underscores the importance of adhering to rigorous infection control procedures, including fully adhering to CDC-recommended decontamination procedures between patients, or using single-patient-use stethoscopes kept in each patient’s room,” senior investigator Dr. Ronald Collman commented. An important question raised by researchers was what quantity of bacteria on a stethoscope was sufficient to cause infection?  The CDC, in its guidelines for disinfection, stated that “medical equipment surfaces” such as stethoscopes should be disinfected with an EPA-registered low- or intermediate-level disinfectant. These guidelines added that “use of a disinfectant will provide an anti-microbial activity that is likely to be achieved with minimal additional cost or work.” The authors noted in their conclusion that these recommended cleaning methods were apparently not routinely followed. In addition to being unable to distinguish between dead versus living bacteria, the molecular methods could not identify drug-resistant strains of the bacteria either, the investigators acknowledged. “Useful future directions would be to use these molecular approaches to identify improved cleaning methods, enhance species-level identification of pathogens, quantify live versus dead bacteria, and define fungal and viral contaminants and shotgun metagenomic sequencing would be useful to analyze drug-resistance genes that might be carried between patients on practitioner stethoscopes,” they concluded.