Getting real with disinfectant concentration and contact time


The processes in place for establishing whether a hospital disinfectant is suitable for use in a clinical setting have been around for a long time - but do they remain fit for purpose? A recent study shows that disinfectant concentration and contact time can be reduced without negatively affecting efficacy - but not too much!

Tests with unrealistically long contact times, high concentrations of disinfectant, and performed in suspension rather than on a hard substrate are not helpful in establishing whether a disinfectant is suitable for use in the clinical setting. Equally, laboratory disinfectant testing needs to be performed with a worst-case scenario in mind. A recent study 'stress tested' the parameters for the laboratory testing of a selection of hospital disinfectants, reducing the disinfectant concentration and contact time. The disinfectants tested were accelerated hydrogen peroxide, quaternary ammonium compounds (QACs), and sodium hypochlorite. There was a degree of tolerance to reducing contact time and disinfectant concentration. The study found that bactericidal efficacy was not reduced when contact times or concentrations were reduced to just below label use values. However, all of the disinfectants were significantly less bactericidal when contact times and concentrations were reduced substantially. The sodium hypochlorite was most tolerant to changes in contact time and concentration.

This study is useful and suggests that contact times and disinfectant concentrations could be reduced in some settings. However, there are many drivers of the efficacy of a disinfectant, including soiling, the presence of biofilms, and stability of the disinfectant. Therefore, laboratory studies need to be complemented by real-world studies in the clinical setting to establish the suitability of disinfectants for surface disinfection in hospitals.


VRE lurking in the ICU environment


An Irish study has identified an established VRE environmental reservoir in the ICU, outside of an outbreak setting. VRE was identified from the ICU environment on 30% of 289 sampling occasions, and a number of patient-environment clusters were identified through molecular typing. A keen focus on the contaminated environment is vital for effective prevention of VRE transmission.

VRE is a Gram-positive pathogen with the capacity to survive on dry environmental surfaces for literally years. There is strong epidemiological evidence that the contaminated environment contributes to the transmission of VRE in clinical settings: being admitted to a room previous used by a patient increases the risk of the next occupant of the same room acquiring VRE.

This study from Ireland presents a comprehensive survey of patient colonisation and environmental contamination with VRE. The team launched an active surveillance programme for VRE colonisation and also took the opportunity to perform prospective surveillance of the environment. VRE colonisation of patients and the environment was common, being detected on 30% of the sampling occasions. Of the 1,647 environment samples collected, 107 sites (6.5%) grew VRE; VRE was (unsurprisingly) more common in isolation rooms (9%) than in open-plan areas (4%). However, the frequent discovery of VRE outside of isolation rooms is concerning. Genotying of the isolates involved identified likely transmission from patients to the environment, and from the environment to patients.

These findings reinforce the importance of contamination of the hospital environment in the transmission of VRE, and argue for enhanced cleaning and disinfection to reduce VRE transmission.



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