Is the stethoscope a fomite for infection?
February 1, 1998 3 minutes read
Is the stethoscope a fomite for infection?
Synopsis: Cultures revealed that most stethoscopes harbored potentially pathogenic bacteria, with coagulase-negative staphylococcus the predominant isolate. Cleaning with an alcohol swab significantly decreased bacteria counts.
Source: Marinella MA, et al. Arch Intern Med 1997; 157:786-790.
Nosocomial infections are a significant cause of morbidity and mortality, especially in the intensive care unit (ICU). Recent outbreaks of nosocomial infections have been linked to contaminated medical devices, including electronic thermometers, latex gloves, and blood pressure cuffs. Stethoscopes can also serve as reservoirs for microorganisms that could be transferred to the skin after contact with a contaminated stethoscope diaphragm. This study examines this hypothesis.
Marinella and colleagues performed aerobic and anaerobic bacterial cultures on 40 stethoscopes randomly selected from physicians, nurses, medical students, and house staff working in an ICU (n = 20) or general medical ward (n = 20) of a large university hospital. In addition, they assessed effects of various cleaning agents on bacterial survival and the transmissibility of Micrococcus luteus, selected for its morphologic characteristics, from inoculated stethoscopes to human skin. Eleven genera and species of organisms were isolated, with coagulase-negative staphylococcus present on 100% of the stethoscopes and Staphylococcus aureus on 38%. Gram-negative organisms were isolated rarely, and none were enteric organisms. Clostridium difficile was not isolated from any stethoscope.
The mean (mean + SE) number of colony-forming units was 158 + 33 per diaphragm and 289 + 54 per rim. Physicians in the ICU had a significantly (P = 0.04) higher load of total bacteria on their stethoscopes than nurses did. Physicians also had a significantly (P = 0.02) higher number of colony-forming units of coagulase-negative staphylococci compared to nurses. Isopropyl alcohol (Webcol Alcohol Prep) significantly (P = 0.02) reduced the mean bacterial load from 158 + 33 to 0.2 + 0.2 colony-forming units on the diaphragm and from 289 + 54 to 2.2 + 1.5 colony-forming units on the rim. Cleaning with soap and water was not effective. All attempts to transfer M. luteus to human skin were successful, demonstrating that stethoscope-to-skin transfer can occur. Thus, it is likely that other bacteria can be transferred as well.
Comment by Leslie A. Hoffman, RN, PhD, medical-surgical nursing chair, Department of Acute/Tertiary Care, University of Pittsburgh School of Nursing.
Stethoscopes have previously been shown to harbor various organisms on their diaphragm surfaces, with coagulase-negative staphylococcus the predominate isolate. In this study, coagulase-negative staphylococcus was again the predominate isolate, both from the stethoscope diaphragm and the plastic rim. Of additional concern, the study demonstrated that bacteria can be transferred from the stethoscope to the skin.
To demonstrate transmission, a strain of M. luteus, which produces a distinct yellow pigment, was chosen. Prior to testing transfer, control cultures were taken of the stethoscope, and the subject’s forearm was cleaned with three applications of povidone-iodine, followed by one application of isopropyl alcohol. The inoculated stethoscope was then pressed on the subject’s prepared forearm for three seconds, an extremely brief interval. Immediately after removal of the diaphragm, the forearm was again cultured. Three attempts to transfer M. luteus showed transmission. However, small numbers of the organisms were transferred, a finding of some encouragement. Of importance, numbers of bacteria were significantly reduced by cleaning the diaphragm and rim with an alcohol prep, a simple act that takes seconds to perform.
ICU physicians had significantly more bacteria on their stethoscopes than nurses. To determine whether this finding resulted from cleaning practices, the investigators conducted a survey of 74 physicians and 51 nurses that revealed 55% of nurses cleaned their stethoscope at least daily compared with 21% of physicians. Further, nurses were more likely to disassemble their stethoscopes at the time of cleaning.
Findings of this study are important because they indicate that cleaning your stethoscope with an alcohol prep, a simple act that consumes minimal time, can substantially reduce bacterial numbers and, thereby, potentially help to reduce the incidence of nosocomial infection.
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