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

Erscheingsdatum 
September 2019
ISSN 
0195-6701
Autoren 
S Gemein, J Gebel, B Christiansen, H Martiny, L Vossebein, FHH Brill, M Decius, M Eggers, T Koburger-Janssen, M Meckel, S Werner, B Hunsinger, T Selhorst, G Kampf, M Exner
Bibliografische Daten 
Journal of Hospital Infection, Volume 103, Issue 1, Pages 78–84
Abstract 

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.