The effects of temperature and humidity on the biocidal efficacy of copper

Michels et al. conducted laboratory tests studying the effects of temperature and humidity on the biocidal efficacy of copper- and silver-containing materials on MRSA. They used the standard methodology of that time, JIS Z 2801, originally the Japanese Industrial Standard (JIS Z 2801), which utilizes temperatures approximating that of human skin (35°C) and high humidity (>90%) and compared it to situations with lower temperatures (20°C) and lower humidity (20%). Under all test conditions, a >5-log reduction of CFU after 24 h was achieved on copper, although slight differences were seen when changing the temperature and humidity. Their results were a >6.4-log reduction of CFU at 35°C and >90% humidity on copper, which dropped slightly to a >6.1-log reduction when lowering the temperature to 20°C. Testing under lower humidity showed a larger difference: at 20% humidity and 35°C, there was a slightly lower reduction than that at >90% humidity (>5.5-log versus >6.4-log reduction, respectively). Interestingly, silver also demonstrated >6.4- and 5.5-log reductions at high humidity at 35°C and 20°C, respectively; however, this was quickly reduced to a <0.3-log reduction at 24% humidity and 20°C but no log reduction at 20% humidity and 35°C.

As a result of the substantial amount of evidence, copper is the only hard surface material that has been approved by the U.S. Environmental Protection Agency (EPA) to make public health claims under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), a federal law of the United States that is responsible for the governance of pesticides to protect applicators, consumers, and the environment. Registered public health claims are as follows: antimicrobial copper alloys continuously reduce bacterial contamination, antimicrobial copper is able to kill >99.9% of bacteria within 2 h of contact, antimicrobial copper remains effective in killing >99.9% of bacteria after repeated recolonization, and antimicrobial copper inhibits bacterial growth between routine cleaning activities.

（To be continued）

Copy from cmr.asm.org

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