Copper as an Antimicrobial Hard Surface

Copper was first clinically investigated as a biocidal surface material. The first clinical article was written in 1983 by an American physician from Philadelphia, PA, Phyllis J. Kuhn. She involved domestic staff from the local hospital in a small study to increase their awareness of modes of infection. They were given culture plates with instructions to return them with cultures from different sites in the hospital. The test showed that a brass doorknob (67% copper and 33% zinc) had very few bacterial colonies, in contrast to stainless steel doorknobs, with heavy growths of both Gram-positive and Gram-negative bacteria. Repeated experiments using a high inoculum of E. coli, S. aureus, group D Streptococcus, and Pseudomonas sp. showed rapid disinfection on brass and copper, compared to heavy growths on stainless steel and aluminum.

Since then, a number of clinical studies have been carried out in different parts of the world, serving to lend clinical relevance to incorporating copper surfaces into the built environment in order to reduce the resident microbial burden and thereby reduce the risk of infection (the United Kingdom, Germany, the United States, Chile, and South Africa. Work done in a university hospital in Birmingham, United Kingdom, replaced three items in an acute medical ward using copper facsimiles for the toilet seat, tap handles, and door push plates for a period of 10 weeks. Here it was observed that when the ward was sampled for the presence of microorganisms, the copper facsimiles harbored 90% fewer microbes (median values) than the original objects to no microbes at all that could be retrieved. This study was further extended by replacing 14 frequently touched items (trolleys, light pulls, flush handles, overbed tables, dressing trolleys, and commode chairs) for copper-containing items on the same medical ward. Again, these items were compared to noncopper equivalents over a period of 24 weeks. This study showed that all 14 items had a reduced bacterial load and that 8 of the 14 items demonstrated a significant reduction compared to noncopper items. Furthermore, antibiotic-resistant bacteria were significantly less frequently cultured on copper items.

Research conducted in other parts of the world showed similar results. For example, a study in a South African primary health care clinic showed a 71% reduction of CFU on copper surfaces. A study on an oncology/pneumatology and geriatric ward in Germany showed a CFU reduction of 30% on copper and a significantly delayed repopulation compared to standard items. In Chile, copper surfaces were installed in 3 rooms on an intensive care unit (ICU) and compared with 3 control rooms. The mean microbial burden was significantly reduced by 49 to 93% in the copper-containing rooms.

The U.S. army funded a large-scale, multicenter, randomized, controlled trial with the aim to assess the antimicrobial properties of copper surfaces in ICUs. Eight ICU rooms in three different hospitals had the most contaminated surfaces replaced with copper and were matched with control rooms. The average microbial burden was 83% lower on copper surfaces than on noncopper surfaces. In 2011, Casey et al. studied the contamination of copper and stainless steel pens used in the hospital. Fifty copper pens (85% copper and 15% zinc) and 50 stainless steel pens (100% stainless steel) were disinfected and distributed to nurses on two critical care units. After being used for one 12.5-h shift, half of the pens (25 copper and 25 stainless steel pens) were immediately sent to the laboratory for microbial sampling, and the remaining 50 pens were stored for 11 h at room temperature before being sent to the laboratory. They found that upon immediate sampling, there was a nonsignificantly lower number of contaminated copper pens than stainless steel pens (48% and 68%, respectively). After storing the pens for 11 h, a significantly lower number of contaminated copper pens was found (20% versus 72%; P = 0.0005). Likewise, a significantly lower number of CFU was found on copper pens than on stainless steel pens upon immediate testing (median [lower to upper quartiles] of 0 [0 to 4] versus 12 [0 to 20]; P = 0.04) and after 11 h of storage (median [lower to upper quartiles] of 0 [0 to 0] versus 8 [0 to 80]; P = 0.0002). More recently, the microbial burden of a standard stethoscope was compared to that of a similar one with 4 parts replaced with copper-containing parts (diaphragm, binaural tube, and the two ear tubes). Different health care professionals (fellow and resident physicians and pediatric nurse practitioners) alternately used the control and copper stethoscopes for 1 week on four separate occasions. They found significantly lower concentrations of bacteria on copper stethoscopes than on the control ones (11.7 versus 127.1 CFU; P < 0.00001). Salgado et al. were the first to report a study on the effect of copper surfaces on the incidence of HAIs. During the study period of almost 1 year, patients were randomly placed into rooms with or without copper touch surfaces. The incidence of HAI and/or MRSA or VRE colonization in ICU rooms with copper showed a significant reduction of 42%, and the incidence of HAI alone was 58% lower in copper rooms than in the control rooms.

All the studies mentioned above provide substantial evidence of the antimicrobial and infection prevention abilities of copper surfaces in clinical settings.

（To be continued）

Copy from cmr.asm.org

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