Efficacy of five 'sporicidal' surface disinfectants against Clostridioides difficile spores in suspension tests and 4-field tests.

BACKGROUND: A sporicidal surface disinfection is recommended both for the outbreak and the endemic setting but a comparative evaluation on the efficacy of 'sporicidal' surface disinfectants using suspension tests and 4-field tests has not been performed. AIM: To determine the efficacy of five 'sporicidal' surface disinfectants (three ready-to-use wipes (A, B, E), two concentrates (C, D) based on peroxides or aldehydes against C. difficile spores. METHODS: The efficacy was determined under clean conditions using a suspension test and the 4-field test. Each test was performed in duplicate in two separate laboratories. Wipes were wrung to collect the solution for the suspension tests. RESULTS: Product A (peracetic acid; 5 min), product C (peracetic acid; 2% solution in 15 min or 1% solution in 30 min) and product D (peracetic acid; only 2% solution in 15 min) were effective with at least a 4 log10-reduction of C. difficile spores in suspension and on surfaces. Product B (hydrogen peroxide) was not effective in suspension (0.9 log10 after 15 min; 3.2 log10 after 1 h) and on surfaces (2.8 log10 after 15 and 60 min). Product E based on glutaraldehyde, (ethylendioxy)dimethanol and DDAC demonstrated 0.9 log10 after 4 h in suspension and 4.5 log10 after 4 h on surfaces. CONCLUSIONS: Not all surface disinfectants with a sporicidal claim were effective against C. difficile spores in standardized suspension tests and in the 4-field test. In clinical practice preference should be given to products that reliably pass the efficacy criteria of both types of tests.

Interlaboratory reproducibility of a test method following 4-field test methodology to evaluate the susceptibility of Clostridium difficile spores.

BACKGROUND: Sporicidal surface disinfection is recommended to control transmission of Clostridium difficile in healthcare facilities. EN 17126 provides a method to determine the sporicidal activity in suspension and has been approved as a European standard. In addition, a sporicidal surface test has been proposed. AIM: To determine the interlaboratory reproducibility of a test method for evaluating the susceptibility of a C. difficile spore preparation to a biocidal formulation following the 4-field test (EN 16615 methodology). METHODS: Nine laboratories participated. C. difficile NCTC 13366 spores were used. Glutaraldehyde (1% and 6%; 15 min) and peracetic acid (PAA; 0.01% and 0.04%; 15 min) were used to determine the spores' susceptibility in suspension in triplicate. FINDINGS: One-percent glutaraldehyde revealed a mean decimal log10 reduction of 1.03 with variable results in the nine laboratories (0.37-1.49) and a reproducibility of 0.38. The effect of 6% glutaraldehyde was stronger (mean: 2.05; range: 0.96-4.29; reproducibility: 0.86). PAA revealed similar results. An exemplary biocidal formulation based on 5% PAA was used at 0.5% (non-effective concentration) and 4% (effective concentration) to determine the sporicidal efficacy (4-field test) under clean conditions in triplicate with a contact time of 15 min. When used at 0.5% it demonstrated an overall log10 reduction of 2.68 (range: 2.35-3.57) and at 4% of 4.61 (range: 3.82-5.71). The residual contamination on the three primarily uncontaminated test fields was <50 cfu/25 cm2 in one out of nine laboratories (0.5%) and in seven out of nine laboratories (4%). CONCLUSION: The interlaboratory reproducibility seems to be robust.

Sampling time effects in the ACT device.

The signal-dependent sampling process in an acoustic charge transport (ACT) device is demonstrated. Theoretical calculations and experimental measurements show the direct effect of gate voltage, wave amplitude, and transport depth on the sampling interval. A decrease in gate voltage and transport depth, and an increase in wave amplitude, are shown to reduce the increase in sampling time delay for a fixed transport current. An analysis of the distortion generated by this nonuniform sampling is performed, and a channel-current-intercept value is computed for a typical ACT device.

Analysis of an interferometer with acoustic surface waves on one mirror.

It has been demonstrated that surface waves propagating on one mirror of an interferometer form an optical diffraction grating. Experimentally confirmed analyses of an interferomet er with 95.5% reflectivity mirrors now indicate that a surface wave power density of 0.028 mW/mm.MHz is required to diffract 1% of transmitted light into the first order beam. This power can be diminished by a factor of more than 20 by increasing the mirror reflectivity to 99%.