Why is there a discrepancy between laboratory test results and real-world efficacy of continuously active quaternary ammonium disinfectants?

To the Editor—Continuously active quaternary ammonium disinfectants containing polymer coatings that bind to surfaces have been developed to provide persistent antimicrobial activity between episodes of cleaning.1,2 Environmental protection agency (EPA) registration as a disinfectant with 24-hour residual antimicrobial activity requires demonstration of a 5-log reduction in bacteria and/or a 3-log reduction in viruses within 10 minutes after 12 cycles of alternating wet and dry abrasions intended to simulate routine contacts that might occur between cleaning episodes.1,3,4 A product registered with the EPA as Firebird F130 (Microban Products, Huntersville, NC) and previously marketed by Professional Disposables International as Sani-24 has demonstrated residual activity against several bacterial pathogens and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).1,5 However, real-world assessments of these products have yielded mixed results.1 In a recent randomized trial, a continuously active disinfectant significantly reduced total bioburden and recovery of clinically important pathogens,6 whereas no significant reductions occurred in another randomized trial.7 Why might there be a discrepancy between laboratory results and real-world efficacy of continuously active quaternary ammonium disinfectants? The product may dry quickly on surfaces because it contains 68.6% ethanol and might require reapplication to achieve 1 minute of wet contact time. [...]we compared the amount of product applied using Sani-24 Germicidal Spray and presaturated Sani-24 Germicidal Wipes with different wiping methods and tested for activity against methicillin-resistant Staphylococcus aureus (MRSA). Sani-24 was applied to overbed tables using 5 methods: (1) spraying with Sani-24 Germicidal Spray following the manufacturer’s recommendation (ie, 3 sprays at 15 cm) providing ∼120 seconds of wet contact time, (2) wiping with 1 Sani-24 Germicidal Wipe with 2 passes over the surface providing ∼60 seconds of contact time, (3) wiping with 1 Sani-24 Germicidal Wipe with 1 pass over the surface providing ∼30 seconds contact time, (4) wiping with 2 Sani-24 Germicidal Wipes to thoroughly wet the surface providing ∼120-seconds contact time, and (5) and wiping with 1 Sani-24 Germicidal Wipe that had first been applied to a 1.2 m2 surface area resulting in reduced product application providing ∼10 seconds contact time.