Environmental sampling for MRSA: a note of caution

The effectiveness of existing and modified cleaning regimens in a Welsh hospital

Hospital cleaning currently has a high media profile. The effectiveness of an existing ward-cleaning regimen was assessed at selected sites over a 14 day period and shown to be highly variable. The cleaning regimen was subsequently modified in two stages, both changes involving a rinse stage and substituting cloths with disposable paper towels. One modification continued using the existing detergent; the other replaced detergent with a quaternary ammonium sanitiser. Both modifications yielded significantly lower and more consistent bacterial counts. Assessment of residual organic soil using adenosine triphosphate (ATP) detection demonstrated that failure rates (measurements exceeding benchmark clean value of 500 relative light units (RLU)) fell from 86-100% after existing cleaning methods, to 0-14% after modified cleaning. Maximum ATP readings fell from 163,870 to 2289 RLU. Incorporating a quaternary ammonium sanitiser into the cleaning regimen produced a further slight, but not significant, improvement in cleaning efficacy. These findings suggest that simple improvements can be made to existing cleaning regimens to increase their efficacy.

An evaluation of different methods for the recovery of meticillin-resistant Staphylococcus aureus from environmental surfaces

Although the association between environmental surfaces contaminated with meticillin-resistant Staphylococcus aureus (MRSA) and hospital infection rates is not fully understood, monitoring programmes can provide an objective starting point for the development and assessment of infection control strategies incorporating improved cleaning. There is, however, no universally accepted method for the recovery of MRSA from environmental surfaces, and the aim of this study was to evaluate a selection of currently available methods. Using five clinical isolates of MRSA and seven protocols, known numbers of bacteria were inoculated on to a stainless steel surface and either recovered immediately (without drying or adsorption) or recovered after 30min (with drying at room temperature and adsorption of cells to the surface). Surfaces were either swabbed or sampled directly by contact methods, and four nutritive media (blood, tryptone soya, oxacillin and meticillin-resistant agars) were tested. Relative sampling efficiencies were determined and the sensitivity of each method per 100cm(2) was calculated. Wide variation in the ability to recover MRSA was found between the different protocols. In the recovery of dried (adsorbed) cells, direct contact methods demonstrated higher sampling efficiency than swabs. The sensitivity of all methods was lower in recovering adsorbed cells from surfaces than unadsorbed cells. Sampling methods consistently proved to be more important than the choice of medium. Dipslides coated with selective agar are recommended for recovering MRSA from flat environmental surfaces.