Insights Into Nosocomial Infection and Environmental Contamination

Microbes collect on fabric, objects, and surfaces in the hospital environment, but what role do they play in disease transmission, and how can a more sterile environment be maintained? The current findings sometimes leave us with more questions than answers. Food for thought was presented at a poster session that focused on nosocomial infections and environmental contamination at the joint 48th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy and the Infectious Diseases Society of America 46th Annual Meeting, which convened October 25-28, 2008, in Washington, DC.

Nano-treated neckties fail to live up to claims
A study to evaluate whether carriage of bacteria on physicians’ clothing could be reduced using nano-treated garments found that, no, the technology could not effectively reduce bacteria and that microbes accumulate on garments over the course of the day.

Wendelyn Bosch, MD, a resident in internal medicine, explained that physicians’ neckties have been shown to carry pathogens and may be a reservoir for nosocomial infections. Bosch and colleagues from the Mayo Clinic in Jacksonville, Fla, evaluated whether nano-treated antimicrobial neckties could, as claimed, reduce microbial carriage and, in turn, reduce the incidence of nosocomial infection.¹ The investigative team dispensed nano-treated neckties to 43 physicians who alternated in wearing either nano-treated neckties or untreated neckties from among their personal garments. Swab samples were collected from the knot and bottom of a selection of ties in the morning and afternoon for 4 months. Samples were cultured on trypticase soy agar and incubated for 48 hours at 37°C (98.6°F). Colony-forming units (CFUs) on the plates were then tallied. In the afternoons, participating physicians also completed questionnaires in which they detailed their hospital activities.

Through this exercise, it was learned that on average, a participating physician saw 9 patients per day. Forty-four percent of these physicians regularly examined open wounds and 60% regularly examined central lines and Foley catheters. It was discovered that regardless of whether the necktie was treated, more CFUs were in the culture plates of samples taken in the afternoon than in those taken in the morning (P < .0001). Twice as many bacteria were cultured from samples taken from the knot than from the tip of ties. Of special importance is that more bacteria were apparently present on the nano-treated ties than on the untreated ties, calling into question claims that such ties repel microbes and therefore have antimicrobial utility.

Fortunately, the most prevalent types of bacteria found in the ties were coagulase-negative staphylococci, diphtheroids, and micrococci-all of which were considered to be normal skin flora. No methicillin-resistant Staphylococcus aureus or gram-negative pathogens were identified.

Bosch and colleagues’ take-home message was that a type of nanotechnology, which involves treating cloth fibers with nano-particles, does not necessarily prevent bacteria from adhering to the cloth, and also that the microbial load on a typical physician’s necktie is greater at the end of the day than at the outset. The reason more bacteria are found on a necktie in the afternoon than in the morning, Bosch conjectured, is that physicians repeatedly adjust their ties during the day, cumulatively passing microbes from skin to cloth.

Evidence on whether pathogens can be transmitted via clothing is lacking, concluded Bosch. Nevertheless, she stressed that proper hygiene-specifically hand washing-remains the most appropriate way to reduce transmission of pathogens between clinicians and patients.

Antimicrobial polymers aren’t so great either
An antimicrobial surface polymer, organosiline, used in commercial products such as bandaids, diapers, and shoe insoles, was put to the test in the hospital setting. It did not perform up to par, according to researchers at the University of Maryland in Baltimore.²

Kerri Thom, MD, assistant professor of epidemiology and preventive medicine, and colleagues compared bacterial contamination of environmental surfaces in the 10-bedroom surgical intermediate care unit at the University of Maryland Medical Center. All environmental surfaces in 5 of the 10 rooms were treated with organosiline. The polymer forms a permanent covalent bond when applied to surfaces and is meant to convey antimicrobial properties.

Swab samples were taken from multiple sites in all 10 rooms twice weekly during September and October 2007 and were cultured for the presence of S aureus, enterococci, Acinetobacter baumanii, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli. A total of 20 samples were collected from treated rooms and 23 samples from untreated rooms. At least 1 index bacterial species was identified in 90% of the samples taken from treated rooms compared with 83% of samples taken from the untreated rooms, suggesting that the polymer had no effect on environmental contamination by the bacterial species studied. Thom concluded that additional investigation on the use of antimicrobial polymers is needed.

Copper may be an ideal antimicrobial surface
Copper surfaces were shown to be antimicrobial by researchers from the University Hospitals Birmingham NHS Foundation Trust and Aston University in Birmingham, United Kingdom.³

In a laboratory setting at Aston University, microorganisms, including S aureus, E coli, K pneumoniae, A baumanii, enterococci, and Candida albicans, among others, were applied to copper alloys and stainless steel and their viability was determined. At the same time, copper fixtures, including push plates, clinical sink taps, and toilet seats were installed in a busy medical ward at the University Hospitals Birmingham NHS Foundation Trust. The bacterial contamination of the copper fixtures was compared with that of standard aluminum and plastic fixtures in the same ward, reported Anna L. Casey, PhD, a research scientist at the NHS Foundation Trust. Swab samples were taken from surfaces in the morning and evening for 6 months, processed, and inoculated onto various microbiological media for culturing.

In the laboratory arm of the study, the number of microbes detected on copper alloys was reduced by 99.9% compared with the number detected on stainless steel. In turn, overall microbial counts were 90% lower on copper fixtures than on standard fixtures in the clinical setting. This statistic held true whether samples were taken in the morning or evening. Furthermore, the antimicrobial activity of copper fixtures in the clinical setting was sustained for more than 6 months. The mechanism of action may be attributed to copper’s oxidative properties. “The effect of copper in reducing environmental contamination in the clinical environment was remarkable and may, in turn, reduce the risk of spread of health care–associated infections,” said Dr Casey.

References:

REFERENCES
1. Bosch W, Hedges MS, Cawley JJ, et al. Do nano-treated neckties reduce the carriage of bacterial pathogens from neckties of physicians. Presented at: the joint 48th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy and the 46th Infectious Diseases Society of America Annual Meeting; October 25-28, 2008; Washington, DC.
2. Thom KA, Standiford HC, Johnson JK, et al. Impact of an antimicrobial treatment of environmental surfaces on contaminated by important nosocomial bacteria. Presented at: the joint 48th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy and the 46th Infectious Diseases Society of America Annual Meeting; October 25-28, 2008; Washington, DC.
3. Casey AL, Lambert PA, Miruszenko L, et al. Copper for preventing microbial environmental contamination. Presented at: the joint 48th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy and the 46th Infectious Diseases Society of America Annual Meeting; October 25-28, 2008; Washington, DC.