Antimicrobial copper-alloy touch surfaces

Antimicrobial copper-alloy touch surfaces can prevent frequently touched surfaces from serving as reservoirs for the spread of pathogenic microbes. This is especially true in healthcare facilities, where harmful viruses, bacteria, and fungi colonize and persist on doorknobs, push plates, railings, tray tables, tap (faucet) handles, IV poles, HVAC systems, and other equipment. These microbes can often survive on surfaces for surprisingly long periods of time (sometimes more than 30 days).

The surfaces of copper and its alloys, such as brass and bronze, are antimicrobial. They have an inherent ability to kill a wide range of harmful microbes relatively rapidly – often within two hours or less – and with a high degree of efficacy. These antimicrobial properties have been demonstrated by an extensive body of research. The research also suggests that if touch surfaces are made with copper alloys, the reduced transmission of disease-causing organisms can reduce patient infections in hospital intensive care units (ICU) by as much as 58%.

Antimicrobial properties
Copper alloy surfaces have intrinsic properties to destroy a wide range of microorganisms. In the interest of protecting public health, especially in healthcare environments with their susceptible patient populations, an abundance of peer-reviewed antimicrobial efficacy studies have been and continue to be conducted around the world regarding copper's efficacy to destroy E. coli O157:H7, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus, Clostridium difficile, influenza A virus, adenovirus, and fungi.

Much of this antimicrobial efficacy work has been or is currently being conducted at the University of Southampton and Northumbria University (United Kingdom), University of Stellenbosch (South Africa), Panjab University (India), University of Chile (Chile), Kitasato University (Japan), the Instituto do Mar and University of Coimbra (Portugal), and the University of Nebraska and Arizona State University (US)

In the US, to qualify copper and its alloys as registered antimicrobial substances under that nation's federal pesticide regulations, an extensive additional body of efficacy testing under Good Laboratory Practice guidelines by an EPA-approved laboratory was required by the USEPA. After these tests were concluded in 2008, registrations of 282 different copper alloys were granted.

Clinical trials
Microorganisms are known to survive on inanimate touch surfaces for extended periods of time. This can be especially troublesome in hospital environments where patients with immunodeficiencies are at enhanced risk for contracting nosocomial infections (hospital-borne infections), often with fatal consequences.

Touch surfaces commonly found in hospital rooms, such as bed rails, call buttons, keyboards, touch plates, chairs, door handles, light switches, grab rails, intravenous poles, dispensers (alcohol gel, paper towel, soap), dressing trolleys, and counter and table tops are known to be contaminated with high levels of potentially dangerous bacteria, including Staphylococcus, Methicillin-resistant Staphylococcus aureus (MRSA), one of the most virulent strains of antibiotic-resistant bacteria and Vancomycin-resistant Enterococcus (VRE). Objects in closest proximity to patients have the highest levels of staphylococcus, MRSA, and VRE. This is why touch surfaces in hospital rooms can serve as abundant sources, or reservoirs, for the spread of bacteria from the hands of healthcare workers and visitors to patients.

Hand and surface disinfection practices are the first line of defense against infection. However, these have fallen short of expectations as opportunistic organisms put patients and healthcare workers at risk. Since approximately 80% of infectious diseases are known to be transmitted by touch, and pathogens found in healthcare facilities can survive on inanimate surfaces for days and even months, the microbial burden of frequently touched surfaces is believed to play a significant role in infection causality. Surfaces in hospitals and healthcare facilities are frequently touched and therefore could become reservoirs of infection.

To evaluate their effectiveness as secondary infection control measures, these products have been made from copper and its alloys and deployed in hospital geriatric wards, intensive care units, and general medical wards around the world.

Clinical trials are being conducted on microbial strains unique to individual healthcare facilities around the world to evaluate to what extent copper alloys can reduce the incidence of infection in hospital environments.

The success of these clinical trials to date, which are summarized here, are prompting hospitals around the world to specify antimicrobial copper touch surfaces as an additional weapon in the fight against infection.

Chile
In Chile, 70,000 nosocomial infections are reported each year, most commonly from common hospital-borne pathogens such as S. aureus, P. aeruginosa and A.baumanii.

In a 30-week clinical trial at the Hospital del Cobre (which incidentally means "Copper Hospital", after a site in Cuba), in Calama, extensive microbial analyses were implemented at the facility's intensive care unit (ICU). Nine hundred ninety copper surfaces from 90 rooms containing 6 different copper objects were studied against an equivalent number of rooms and surfaces containing non-copper objects. Over-the-bed tables were made from copper alloy C70600. Bedrails were clad with copper alloy C11000 foils. Visitor chairs were fitted with copper alloy C70600 armrests. Copper alloy C71000 intravenous poles were provided. Writing pens used to input data on a touch screen were made from brass (70% Cu, 30% Zn).

Results of this clinical trial demonstrated an approximately 90% reduction of microorganisms on the copper items compared to the controls after ten weeks. A reduction in the total microbial burden was seen for each class of microbe evaluated. Furthermore, continuous antimicrobial activity of copper persisted throughout the study.

Copper was effective in reducing microbial loads on all 6 surfaces tested (i.e., bed rails by 91%, bed levers by 82%, tray tables by 83%, chair arms by 92%, monitor pen by 49%, and IV poles by 88%).

Average microbial burden counts in rooms with copper touch surfaces were significantly lower than in rooms without copper surfaces. Staphylococci were the most predominant microorganism isolated and copper was effective in reducing the Staphylococci microbial burden. Further studies regarding the clinical implications of copper's intrinsic ability to reduce microbial burdens in hospitals are being planned.

Japan
Researchers from the Kitasato University School of Medicine conducted antimicrobial studies of S. aureus, E. coli, and P. aeruginosa on various Japanese copper alloy coins and on copper alloy plates. The microbes were strains from hospital environments. Copper and its nickel-silver, cupronickel, and brass alloys were found to kill the bacteria within a short time. In another experiment, bacterial colonies were investigated on ball point pens made with and without copper alloys. Total bacterial colonies on the copper pens were much lower than on the non-copper pens: 2.1 CFU versus 47.8 CFU. Staphyloccocus counts on copper ball point pens were also much lower: 0.7 CFUs versus 20.8 CFUs on non-copper pens.

Due to the success of these results, a 2-year clinical trial was conducted to monitor contamination levels of nosocomial bacteria in the dermatology ward and neonatal intensive care unit (NICU) at Kitasato University Hospital. The antimicrobial efficacy of copper on floors, sinks, push plates, showerheads and doorknobs was evaluated by comparing bacterial loads on these surfaces and on their non-copper counterparts.

The number of viable Staphylococcus spp. organisms on surfaces containing copper and its alloy were reduced by half to one-thirtieth of that on control surfaces, depending upon surface humidity and the frequency of contact. Similar definitive findings were also obtained for Pseudomonas aeruginosa.

Various metals were evaluated for their antimicrobial efficacies, including copper alloys, zinc, nickel, tin, silver, and gold. Antimicrobial efficacies generally followed Lewis acidity values of the various metals. Silver, a prohibitively expensive precious metal, had the highest bactericidal activity; copper came in second. The study also found that contact dermatitis allergies rarely occur if copper is used as a hygienic touch material.

The bactericidal activity of copper was also tested against two strains of MRSA and S. aureus in vitro to determine whether copper alloys are effective in preventing the spread of contamination on the touch surface products used in the hospital ward. MRSA and S. aureus counts fell below detection limits within 180 minutes. The results indicated that copper has a strong bactericidal effect against S. aureus, including MRSA.

When a copper plate was situated on a MRSA-infected floor in the dermatology ward around a bed of a MRSA-infected patient, the bacterial count of S. aureus, including MRSA and the other Staphylococcus on the floor covered with a copper plate was significantly less than on a floor unprotected by copper alloys. These results suggested that the copper plate helped to prevent the spread of MRSA contamination in the hospital.

South Africa
Multidrug-resistant and extremely drug-resistant Mycobacterium tuberculosis (MTB) is responsible for the spread of tuberculosis in South African hospitals. Test strains of Candida albicans, Pseudomonas aeruginosa, Klebsiella pneumoniae meticillin-resistant Staphylococcus aureus (MRSA), and MTB were isolated from South African patients at a hospital's intensive care unit in order to establish the minimum in-vitro copper concentrations to produce sterilization against these microbes and yeast. Acinetobacter baumannii was isolated from a patient in a burn unit and two clinical strains of MTB were collected and tested.

Copper and its alloys demonstrated antimicrobial activities against multiple-antibiotic-resistant nosocomial bacteria and C. albicans isolated from the hospital, whereas stainless steel and PVC did not. Copper and its alloys showed a marked inhibitory effect (88–98%) on MTB despite the strain's drug resistance. The researchers concluded that the minimum concentration of copper to be an effective antimicrobial agent is >55% for yeasts and bacteria. Higher concentrations of copper were found to be necessary to inhibit MTB.

United Kingdom
In the United Kingdom, around 300,000 patients contract nosocomial infections each year and at least 5,000 patients die of complications from infections contracted in hospitals.

For these reasons, a cross-over clinical trial (a test method designed to eliminate variability bias from patients, staff, cleaning efficacy, outbreaks, etc.) evaluating antimicrobial copper alloys was carried out at Selly Oak Hospital over an 18-month period in 2007–2008 by the University Hospital Birmingham NHS Trust and Aston University.

Frequently touched surfaces typically manufactured with standard materials (i.e., plastic, chrome, aluminum) were replaced with copper alloys. These included a copper alloy set of sink tap handles (60% Cu, 40% Zn) and a ward entrance door push plate (70% Cu, 30% Zn).

Contamination reductions of 90–100% were observed for Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumanii, Enterococcus spp., and Candida albicans on the copper alloy surfaces versus the non-copper standard surfaces. A microorganism reduction of 100% was observed on the hot tap copper alloy handle.

The high degree of clinical performance suggested that copper alloy surfaces may increase the effectiveness of existing infection control practices and may lower the risk of infections acquired in healthcare facilities.

Based on the results of this and other laboratory and clinical studies, St. Francis Private Hospital, a 140-bed facility located in Mullingar, County Westmeath, Ireland, decided to become the first hospital in the world to fully specify hygienic copper door handles throughout its facility as part of its infection control program. A full upgrade of all door furniture (i.e., 250 doorsets, incorporating handles, push plates and privacy locks) to antimicrobial copper in the hospital and nursing home commenced in January 2010.

Healthcare architects in the United Kingdom are now specifying antimicrobial copper. Refurbishment projects specifying copper products are anticipated across NHS Trust facilities.

United States
In the US, a high degree of statistical significance is needed to provide a convincing argument to U.S. federal government healthcare authorities, such as the Centers for Disease Control and Prevention (CDC), regarding the effectiveness of copper alloys in reducing microbial loads and cross infection in healthcare environments. For this reason, clinical trials at three major US hospitals are currently examining environmental bacterial loads, infection rates, and impacts on cross-contamination in intensive care unit (ICU) rooms retrofitted with copper touch surfaces versus rooms without copper surfaces.

The trials are funded by the U.S. Department of Defense (DOD) under the Telemedicine and Advanced Technology Research Center (TATRC), a subordinate element of the United States Army Medical Research and Materiel Command (USAMRMC). DOD has extraordinary interests in the potential for antimicrobial copper surfaces to reduce hospital-acquired infections because it wants to prevent hospital-acquired infections among thousands of its enlisted armed forces servicemen and servicewomen who have been injured in recent conflicts. TATRC, which funds a Military Infectious Disease Program has been granted funds by the United States Congress to evaluate the antimicrobial effectiveness of copper, brass and bronze alloys. The studies are coordinated through the Advanced Technology Institute in Charleston, South Carolina.

Four-year clinical studies, published in 2013, were conducted at the intensive care units (ICUs) at Memorial Sloan-Kettering Cancer Center in New York City, one of the world's most prestigious cancer facilities, the Medical University of South Carolina, and the Ralph H. Johnson VA Medical Center in Charleston, South Carolina.

The studies revealed that the use of antimicrobial copper surfaces in the ICU's reduced the number of healthcare-acquired infections (HAIs) by 58% compared to patients treated in ICUs with non-copper touch surfaces. The antimicrobial copper surfaces were proved to work continuously.

An evaluation of the microbial burden of various objects in the ICU rooms has also been documented and is available.

Earlier results disclosed in 2011 indicate that the coppered rooms demonstrated a 97% reduction in surface pathogens versus the non-coppered rooms. This reduction is the same level achieved by "terminal" cleaning regimens conducted after patients vacate their rooms. Furthermore, of critical importance to health care professionals, the preliminary results indicated that patients in the coppered ICU rooms had a 40.4% lower risk of contracting a hospital acquired infection versus patients in non-coppered ICU rooms. The U.S. Department of Defense investigation contract, which is ongoing, will also evaluate the effectiveness of copper alloy touch surfaces to prevent the transfer of microbes to patients and the transfer of microbes from patients to touch surfaces, as well as the potential efficacy of copper-alloy based components to improve indoor air quality.

The latest results from the studies at the three institutions will be developed into a manuscript for publication.

In a separate initiative not funded by the U.S. Department of Defense, clinical trials at an infectious disease outpatient ward consisting of patients with HIV and other infectious diseases are being conducted at North Shore University Hospital in Manhasset, New York. An alloy of 90% Cu 10% Ni significantly lowered the microbial burden, primarily Staphylococci, on arm surfaces of phlebotomy chairs versus wooden arm surfaces. The median reduction for total bacteria on the copper alloy chairs arms was 90%. Use of the chair with copper arm tops resulted in a 17-fold lower risk of exposure to environmental microbes than when patients used the standard chair. The majority of the samples from the chairs with copper components were below the 500 CFU/ cm2 level believed to represent a risk to hospital patients. The microbiocidal properties of the copper chair arms were able to confer an 'antimicrobial halo' within the general vicinity of the arm top. The microbial burden associated with the wooden side arms of the copper covered chair arms was 70%, lower than those on the control chair. This halo effect may help to help reduce the transfer of pathogenc bacteria.

Similarly, patients and healthcare workers who used chairs with copper trays were subjected to a 15-fold lower risk than the patients using chairs with composite trays. The microbial burden on copper trays was reduced by 88% compared to the composite plastic surface.

A study completed in April 2011 analyzed the effectiveness of copper-alloy furnishings to lessen the microbial load on various frequently touched surfaces such as door handles, toilet seats, and railings. Of the 14 surfaces tested 8 had statistically significant decreases in the number of microbes found on them while the other 6 had a decrease in the number of microbes as well, but not in a statistically significant amount. Additionally certain microbes in particular were found in far less quantities on the copper-alloy surfaces than on the normal ones, these being Vancomycin-resistant Enterococcus, Staphylococcus aureus, and Coliform bacteria. The study concluded that copper surfaces may be an effective adjunct to safe hygiene practices in a hospital setting.

The antimicrobial halo effect of copper surfaces
Copper surfaces have an antimicrobial 'halo' effect on surrounding non-copper materials. This effect is also helpful in reducing the presence of bacteria in healthcare environments. Research implemented in the neonatal intensive care unit (ICU) at Aghia Sofia Children's Hospital in Greece showed that non-copper surfaces up to 50 centimeters from the antimicrobial copper surfaces exhibited a microbial reduction of 70% compared to surfaces not in such close proximity. The halo effect was first observed during in trials at a US outpatient clinic in 2010.

USEPA registrations of antimicrobial copper alloy touch surfaces
On February 29, 2008, the United States Environmental Protection Agency (EPA) approved the registrations of five different groups of copper alloys as “antimicrobial materials” with public health benefits. The EPA registrations now cover 479 different compositions of copper alloys within six groups (an up-to-date list of all approved alloys is available). All of the alloys have minimum nominal copper concentrations of 60%. The results of the EPA-supervised antimicrobial studies demonstrating copper's strong antimicrobial efficacies across a wide range of alloys have been published.

These copper alloys are the only solid surface materials to be granted “antimicrobial public health claims” status by EPA. Before these registrations were granted, only antimicrobial gases, liquids, sprays, and concentrated powders, including sterilizers, disinfectants and antiseptics, were registered to make antimicrobial public health claims.

Microbes tested and killed in EPA laboratory tests
The bacteria destroyed by copper alloys in the EPA-supervised antimicrobial efficacy tests include:
 * Escherichia coli O157:H7, a foodborne pathogen associated with large-scale food recalls.
 * Methicillin-resistant Staphylococcus aureus (MRSA), one of the most virulent strains of antibiotic-resistant bacteria and a common culprit of hospital- and community-acquired infections.
 * Staphylococcus aureus, the most common of all bacterial staphylococcus (i.e., Staph) infections that cause life-threatening disease, including pneumonia and meningitis.
 * Enterobacter aerogenes, a pathogenic bacterium commonly found in hospitals that causes opportunistic skin infections and impacts other body tissues.
 * Pseudomonas aeruginosa, a bacterium in immunocompromised individuals that infects the pulmonary and urinary tracts, blood and skin.
 * Vancomycin-resistant Enterococcus (VRE), a pathogenic bacterium that is the second leading cause of hospital-acquired infections.

EPA test protocols for copper alloy surfaces
The registrations are based on studies supervised by EPA which found that copper alloys kill more than 99.9% of disease-causing bacteria within just two hours when cleaned regularly (i.e., the metals are free of dirt or grime that may impede the bacteria's contact with the copper surface).

To attain the EPA registrations, the copper alloy groups had to demonstrate strong antimicrobial efficacies according to all of the following rigorous tests:
 * Efficacy as a sanitizer: This test protocol measures surviving bacteria on alloy surfaces after two hours.
 * Residual self-sanitizing activity: This test protocol measures surviving bacteria on alloy surfaces before and after six wet and dry wear cycles over 24 hours in a standard wear apparatus.
 * Continuous reduction of bacterial contamination: This test protocol measures the number of bacteria that survive on a surface after it has been re-inoculated eight times over a 24-hour period without intermediate cleaning or wiping.

EPA registered antimicrobial copper alloys
The alloy groups tested and approved were C11000, C51000, C70600, C26000, C75200, and C28000.

The EPA registration numbers for the six groups of alloys are as follows:

Claims granted by EPA in antimicrobial copper alloy registrations
The following claims are now legally permitted when marketing EPA-registered antimicrobial copper alloys in the US:

The registrations state that “antimicrobial copper alloys may be used in hospitals, other healthcare facilities, and various public, commercial and residential buildings.”

Public health claims granted by EPA in antimicrobial copper alloy registrations
The EPA copper alloy registrations were granted “with public health claims,” meaning that they permit manufacturers of copper-based products sold in the U.S. to claim on their labels the ability of copper, brass, and bronze to kill harmful, potentially deadly bacteria.

Product stewardship requirements of EPA
As a condition of registration established by EPA, the Copper Development Association (CDA) in the US is responsible for the product stewardship of antimicrobial copper alloy products. CDA must ensure that manufacturers promote these products in an appropriate manner. Manufacturers must only promote the proper use and care of these products and must specifically emphasize that the use of these products is a supplement and not a substitute to routine hygienic practices.

EPA mandated that all advertising and marketing materials for antimicrobial copper products contain the following statement:

Antimicrobial copper alloys are intended to provide supplemental antimicrobial action in between routine cleaning of environmental or touch surfaces in healthcare settings, as well as in public buildings and the home. Users must also understand that in order for antimicrobial copper alloys to remain effective, they cannot be coated in any way.

CDA is currently implementing an outreach program through written communications, a product stewardship website, and through a Working Group which meets periodically to expand educational efforts.

More than 100 different potential product applications were cited in the registrations for their potential public health benefits.

EPA warranty statement
The EPA warranty statement is worded as follows:

Note: With the exception of the product name and the percentage of active ingredient, the EPA-approved Master Labels for the six groups of registered alloys are identical.

U.S. Market
Antimicrobial Copper (Cu+) is a logo/mark required by the U.S. E.P.A. in order for bulk metal fabricators and manufacturing companies to make public health claims about antimicrobial copper in the U.S. market. The logo/mark indicates that the products have strong efficacies as sanitizers, residual self-sanitizing efficacies after multiple wet-dry cycles, and continuous reductions of bacterial contaminants.

A list of bulk alloy suppliers that offer E.P.A.-registered antimicrobial copper to manufacturers is available.

An list of approved manufacturers and retailers offering antimicrobial copper products to the regulated U.S. market is also available. These firms have completed all legal requirements to sell antimicrobial copper products in accordance with the U.S. E.P.A registrations. Products offered by the approved companies include sinks, keyboards, faucets, IV poles, tables, stretcher rails, railings, hampers, decorative and architectural hardware (levers, grips, knobs, pulls, towel bars, grab bars, kick plates, bath accessories, outlet covers, light switch covers), laboratory incubators, cabinet hardware, decorative tile, and free weights.

The U.S. E.P.A. oversees a stewardship plan to promote the responsible use of Antimicrobial Copper. A guidance document detailing the proper use and care of antimicrobial Copper Alloys is available. Further information about the making accurate claims about Antimicrobial Copper is also available.

Approved products
Many antimicrobial copper alloy products have been approved for registration in healthcare facilities, public and commercial buildings, residences, mass transit facilities, laboratories, and play area equipment in the U.S. A complete list of registered products is available from EPA.

Peer-reviewed research

 * H. T. Michels, J. O. Noyce, and C. W. Keevil; Effects of Temperature and Humidity on the Efficacy of Methicillin-resistant Staphylococcus Aureus Challenged Antimicrobial Materials Containing Silver and Copper; Letters in Applied Microbiology, 49 (2009) 191–195
 * H. T. Michels and D. G. Anderson; Antimicrobial regulatory efficacy testing of solid copper alloy surfaces in the US; pp 185–190, Metal Ions in Biology and Medicine: Vol. 10., Eds Ph. Collery, I. Maymard, T. Theophanides, L. Khassanova, T. Collery. John Libbey Eurotext, Paris © 2008
 * L. Weaver, H. T. Michels, and C. W. Keevil; Survival of Clostridium difficile on copper and steel: futuristic options for hospital hygiene, Journal of Hospital Infection, Vol. 68, Issue 2, p. 145-151, February 2008
 * H. Michels, W. Moran and J. Michel; Antimicrobial Properties of Copper Alloy Surfaces, with a Focus on Hospital-Acquired Infections, International Journal of Metalcasting, Summer 08, pp 47–56, 2008
 * S. Mehtar, I. Wiid, and S.D. Todorov; The antimicrobial activity of copper and copper alloys against nosocomial pathogens and Mycobacterium tuberculosis isolated from healthcare facilities in the Western Cape: an in-vitro study; Journal of Hospital Infection, Vol. 68, Issue 1, p 45-51, January 2008
 * H.T. Michels, D.G. Anderson, J.O. Noyce, S.A. Wilks and C.W. Keevil; The Antimicrobial Properties of Copper Alloys and Their Potential Applications; Proceedings of the Sixth International Copper-Cobre Conference, p. 121-133, Vol. I, August 2007
 * J. O. Noyce, H. Michels and C.W. Keevil; Inactivation of Influenza A Virus on Copper versus Stainless Steel Surfaces; Applied and Environmental Microbiology, p. 2748 – 2750, Vol. 73, No. 8, April 2007
 * H. T. Michels, Anti-Microbial Characteristics of Copper; ASTM Standardization News, October 2006.
 * J. O. Noyce, H. Michels and C. W. Keevil; Potential use of copper surfaces to reduce survival of epidemic Methicillin-resistant Staphylococcus aureus in the healthcare environment, Journal of Hospital Infection, Vol. 63, Issue 3, p. 289-297, July 2006
 * H. T. Michels, J. P. Noyce, S. A. Wilks and C. W. Keevil; Copper Alloys for Human Infectious Disease Control; Copper for the 21st Century, Materials Science & Technology 2005 (MS&T’05) Conference, Pittsburgh, PA, September 25–28, 2005, ASM, ACerS, AIST, AWS, TMS, ISSN: 1546-2498
 * S. A. Wilks, H. Michels and C. W. Keevil; The Survival of Escherichia coli O157 on a range of metal surfaces; International Journal of Food Microbiology, 105 (2005), p. 445-454.
 * H. T. Michels; Copper Alloys May Be Allies in Fight Against Germs; in Plumbing Standards-An Official Publication of the American Society of Sanitary Engineers, October–December 2004
 * H. T. Michels, S. A. Wilks and C. W. Keevil; Effects of Copper Alloy Surfaces on the Viability of Bacterium, E. coli 0157:H7; The Second Global Congress Dedicated to Hygienic Coatings & Surfaces, Orlando, Florida, US, January 26–28, 2004, Paper 16, Published by Paint Research Association, Middlesex, UK, ISBN 0-9543164-5-2, 2004.
 * H. T. Michels, S. A. Wilks and C. W. Keevil; The Antimicrobial Effects of Copper Alloy Surfaces on the Bacterium E. coli 0157:H7; Proceedings of Copper 2003 – Cobre 2003, The 5th International Conference, November 30 – December 2, 2003, Santiago, Chile, Vol. 1 – Plenary Lectures, Economics and Applications of Copper, pp. 439–450, A Publication of The Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, Quebec, Canada, 2003
 * P. J. Kuhn; Doorknobs: a source of nosocomial infection?; Diagnostic Medicine, 1983.