Background:

Stethoscope diaphragms have been shown to harbor potentially pathogenic bacteria.

Objectives:

To assess bacterial contamination on the diaphragm and under the plastic rim that secures the diaphragm of stethoscopes of physicians, nurses, medical students, and house staff in an intensive care unit and a general medical ward of a large university hospital. Also to compare the effectiveness of various cleaning agents and assess the transmissibility of bacteria from contaminated stethoscopes to human skin.

Methods:

Aerobic and anaerobic bacterial cultures were performed on 40 randomly selected stethoscopes. We compared the effects of isopropyl alcohol, sodium hypochlorite (bleach), and benzalkonium chloride swabs, as well as soap and water, on reducing bacterial contamination on the stethoscope diaphragm and under the rim. The transmissibility ofMicrococcus luteusinoculated onto a stethoscope diaphragm to clean human skin was also determined.

Results:

Eleven genera and species of bacteria were isolated, with coagulase-negative staphylococcus present on 100% of stethoscopes andStaphylococcus aureuson 38%.Clostridium difficilewas not isolated. The mean (±SE) number of total colony-forming units was 158± 33 per diaphragm and 289 ±54 per rim. Physicians' stethoscope diaphragms had significantly more colony-forming units of coagulase-negative staphylococci than those of nurses: 163±44 vs 50±12, respectively (P=.02). The most effective cleaning agent was isopropyl alcohol: after cleaning the diaphragm surface, the stethoscope diaphragms contained 0.2±0.2 colony-forming units and the rims contained 2.2±1.5 colony-forming units (P=.01). In addition,M luteuswas transferred from inoculated stethoscopes to human skin.

Conclusions:

Most stethoscopes harbor potential pathogens but are not a source ofC difficile. Physicians' stethoscopes generally had a higher bacterial load than nurses' stethoscopes. Isopropyl alcohol is an effective cleaning agent when applied to the stethoscope diaphragm. Stethoscopes transferM luteusto human skin, making it likely that other bacteria can be transferred as well. Arch Intern Med. 1997;157:786-790

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