Comparison of two sampling methods for the detection of gram-positive and gram-negative bacteria in the environment: moistened swabs versus Rodac plates.
The objective of this study was to evaluate the moistened swab technique vs. Rodac plates for detecting Gram-positive and Gram-negative bacteria in the inanimate environment. Over a period of 22 months, the environment of 190 patients infected or colonized with MRSA, VRE or multiresistant Gram-negative bacteria was sampled in turn. MRSA and VRE could be detected with either method in 33 out of 54 (61.1%) patient rooms in 174 out of 706 (24.6%) environmental samples. However, multiresistant Gram-negative bacteria were found in 42 out of 136 (30.9%) rooms with a very low frequency of 89 out of 1827 (4.9%) environmental samples (p < 0.0001). The sensitivity of the swab technique for Gram-positive cocci was 54% (94/174) vs. 69.5% (121/174) for the Rodac plates, ([CI95%], 47-61% vs. 62-76%, p < 0.05). In contrast, the sensitivity of the swab technique for Gram-negative bacteria was 74.2% (66/89) vs. 42.7% (38/89) for the Rodac plates, ([CI95%], 64-83% vs. 32-54%, p < 0.05). In conclusion, environmental contamination with Gram positive cocci is detected more often than with Gram-negative bacteria. For the detection of Gram-positive cocci, Rodac plates are superior to the swab technique; whereas Gram-negative rods can be detected more often by the swab technique. All these results proved to be statistically significant.
Zentralbereich für Krankenhaushygiene, Universitätsklinikum, RWTH Aachen, 52057 Aachen, Germany. slemmen@post.klinikum.rwth-aachen.de
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D015169:Colony Count, Microbial; D003428:Cross Infection / Q000453:epidemiology / Q000517:prevention & control*; D016983:Enterococcus / Q000302:isolation & purification; D004784:Environmental Monitoring / Q000379:methods; D062665:Epidemiological Monitoring; D005858:Germany / Q000453:epidemiology; D006090:Gram-Negative Bacteria / Q000302:isolation & purification*; D006094:Gram-Positive Bacteria / Q000302:isolation & purification*; D006801:Humans; D016106:Methicillin Resistance; D011237:Predictive Value of Tests; D013048:Specimen Handling / Q000379:methods; D013211:Staphylococcus aureus / Q000302:isolation & purification; D020713:Vancomycin Resistance