Establishment of a standardized phase 2/step 2 method for virucidal surface disinfection: results of an interlaboratory ring trial (4-field test).

INTRODUCTION

Evaluating the virucidal efficacy of surface disinfectants under practical conditions with mechanical action remains a major challenge. Current standards primarily rely on suspension tests and carrier tests without mechanical action, whereas mechanical, surface-based methods are not yet sufficiently validated for virucidal testing. This methodological validation study reports the results of an interlaboratory ring trial on the 4-field test for viruses with hard water. The objective of the present study was to validate a practical test method aligned with European standards and to support the development of a new Work Item within the Working Group 1 of CEN Technical Committee 216 activities.

METHODS

Thirteen European and international laboratories tested three human pathogenic model viruses - Adenovirus type 5, Modified Vaccinia Virus Ankara, and Murine Norovirus - on non-porous surfaces in the 4-field test using hard water. Virus recovery was assessed across multiple contact times, and repeatability and reproducibility were calculated according to ISO 13528.

RESULTS

All viruses were reliably recovered on test field 1. The method was largely robust across laboratories, although variations in physical parameters affected interlaboratory consistency, underscoring the relevance of mechanically driven application factors.

CONCLUSION

The virucidal 4-field test demonstrates promising applicability as a phase 2/step 2 method and represents a valuable candidate for incorporation into future European standards. The method is particularly relevant for assessing ready-to-use wipes as virucidal efficacy depends on the combined effects of wipe material, released liquid, and mechanical action, which may substantially differ from results obtained in the absence of mechanical application. Representative-of-use validation methods are therefore essential for assessing disinfectant efficacy in hospitals, long-term care facilities, and public spaces.