Quantification of Staphylococcus aureus and Staphylococcus epidermidis on the hands of health‐care workers using a real‐time polymerase chain reaction method

Abstract

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 (CV_I) was 129% for S. aureus and 62% for S. epidermidis. Inter‐individual biological variation (CV_G) 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 CD_I/√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.

• Biological variation
• critical difference
• index of individuality
• quantitative polymerase chain reaction
• reference interval

Acknowledgements

We thank Jens Nederby Nielsen for his support and helpful advice. This study was supported by Fonden for Lægevidenskabelig Forskning ved Sygehuse m.v. i Vejle Amt (Sundhedsforvaltningen, Damhaven 12, 7100 Vejle).