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Scand J Clin Lab Invest. 2007;67(2):165-77.
Quantification of Staphylococcus aureus and Staphylococcus epidermidis on the hands of health-care workers using a real-time polymerase chain reaction method.
Horn P, Schouenborg PO, Brandslund I.
Department of Clinical Biochemistry, Vejle Hospital, Vejle, Denmark. pebeho@vs.vejleamt.dk
OBJECTIVE: The objective of this study was to test a polymerase chain reaction (PCR) assay intended as a tool for monitoring hand hygiene in hospital wards. METHODS: The hands of 20 health-care workers were sampled for 10 days using real-time PCR for quantification of Staphylococcus aureus and S. epidermidis. Reference intervals (CI) and biological variation were evaluated using index of individuality (II) and critical difference (CD). RESULTS: 45% of the participants were positive for S. aureus on all 10 days. Intra-individual biological variation (CVI) was 129% for S. aureus and 62% for S. epidermidis. Inter-individual biological variation (CVG) was 245% for S. aureus and 107% for S. epidermidis. II was 0.55 for S. aureus and 0.71 for S. epidermidis, indicating a high degree of individuality and limited use of the reference values. A significant individual change was determined at 374% for S. aureus and 211% for S. epidermidis. In an intervention study aimed at better hand hygiene in a ward with n participants, the difference before and after intervention is significant at CDI/sqrt[n] per cent. CONCLUSIONS: The PCR assay can be used to detect change in a group mean of S. aureus and S. epidermidis in a hospital ward, i.e. before and after an intervention to improve hand hygiene. For the individual, the change in bacteria levels needed for significance is compromised by high intra-individual variation.