Does Copper Prevent Nosocomial Transmission of COVID-19?

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has killed more than 1 million people worldwide since early 2020.¹ Age is one of the main risk factors for death from coronavirus disease-2019 (COVID-19).² In France, a third of COVID-19 deaths occurred in long-term accommodation establishments for dependent older people (nursing homes).³

Uncertainties persist on the relative importance of modes of transmission of SARS-CoV-2, but it is widely accepted that it is transmitted by respiratory droplets and by hands (especially through contact with contaminated surfaces).⁴ The relative contribution of airborne versus surface transmission of COVID-19 remains unclear. Several antimicrobial surfaces have been studied and used around the world to prevent human-to-human transmission of SARS-CoV-2. Copper is a metallic element well known for its antimicrobial properties, and in vitro studies have shown that coronaviruses do not survive for a long time on it.^{5 , 6}

A nursing home in France was divided into 2 distinct identical and symmetrical wings. In 2014, one of them was equipped with elements (door handles, handrails, and grab bars) covered with a copper alloy known to be antimicrobial. This structure, with its two identical wings but different by the copper equipment, enables to evaluate the epidemic spread in each wing and to assess the preventive effectiveness of copper.

We therefore carried out a quasi-experimental study within this nursing home to study the preventive efficacy of copper in infections by SARS-CoV-2 and thus improve knowledge on virus transmission by hands. During the study period, corresponding to the COVID-19 epidemic peak of the first semester in France (from March 20, 2020, to May 15, 2020), we systematically recorded the date of the first positive test in reverse transcription polymerase chain reaction (RT-PCR), for each case confirmed. In case of a suspicious infection, later confirmed as positive by serologic tests (false negative RT-PCR),⁷ we chose the date of the negative RT-PCR as the theoretical date of infection. The relative risk and its 95% confidence interval were calculated from the incidence rates of COVID-19 in each wing.

Among the 353 people followed, 47 cases of COVID 19 were recorded (13%) during the study period. The relative risk of infection was significantly higher in the copper-equipped wing (ie, 2.98, 95% confidence interval 1.60-5.89).

These results show that the copper surfaces had no protective effect in preventing the transmission of SARS-CoV-2 and make us question the importance of hand contamination. Recent studies have highlighted the importance of airborne transmission of SARS-CoV-2 via microparticles, and our findings may be additional evidence.⁸ Indeed, if the transmission is mainly aerial, it is logical that the protection offered by copper is not sufficient.

A previous study, carried out in the same nursing home, led to similar conclusions with an epidemic of seasonal influenza (also known to be airborne transmitted), and showed that copper did not appear to have any protective effect, although it was effective in reducing the risk of contamination for manual nosocomial infections, especially bacterial.⁹

In terms of prevention, even if transmission through hands must be combated by regular hand washing, its relative weight is likely to be less than that of transmission by respiratory droplets.