Evaluation of the Efficacy of Copper (100% Cu) and Brass (70% Cu) for Inactivation of a Human Norovirus Surrogate by Porcine Gastric Mucin Binding and Infectivity Assays

Introduction: Human noroviruses (HuNoVs) are the leading cause for foodborne illnesses. Copper and copper alloys have been shown to inactivate many pathogens, including HuNoVs. Due to the difficulty in culturing HuNoVs, studies of inactivation of HuNoVs usually rely on surrogates and assays based on qRT-PCR. However, the accuracy of using assays, based on RT-qPCR, to quantify infectious virus particles for copper and copper alloy treatments is still unclear.

Purpose: This study evaluated the efficacy of copper (100% Cu) and brass (70% Cu) for inactivation of Tulane virus (TV), a suitable surrogate for HuNoV, by both plaque assay and porcine gastric mucin-conjugated magnetic beads (PGM-MB) binding assay followed by RT-qPCR (referred to as PGM-MB/PCR assay).

Methods: TV was inoculated onto and treated on copper and brass coupons for 0, 10, 20, 30, and 40 minutes (three replicates). The virus was eluted at the time points. Eluted viruses were assayed for infectivity by plaque assay or treated by RNase A, bound by PGM-MB and quantified by RT-qPCR (PGM-MB/PCR assay).

Results:  As assessed by plaque assay, a 20-minute treatment by copper achieved a 4.2±0.3 log reduction (P<0.05) of TV, close to the maximum detectable reduction by the assay (4.3±0.2 log reduction). However, no more than 1.0-log reduction was observed from all the copper treatments when PGM-MB/PCR assay was used. Brass treatment for 40 min, only, reduced TV by 1.5±0.3 log (P<0.05) by plaque assay, while for the PGM-MB/PCR assay with the same treatment, no reduction (0.0±0.0 log, P>0.05) was observed.

Significance: These results suggest that copper can rapidly inactivate TV. The PGM/PCR assay would likely underestimate the efficacy of copper and copper alloys for inactivation of HuNoVs.