Comparison of two sampling methods for the detection of Gram-positive and Gram-negative bacteria in the environment: moistened swabs versus Rodac plates

Abstract

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, ([CI 95%], 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, ([CI 95%], 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.