Pilot study on the microbial contamination of conventional vs. silver-impregnated uniforms worn by ambulance personnel during one week of emergency medical service.

The antimicrobial impregnation of products used everyday, such as surfaces, textiles and clothing - including those used in hospitals - is increasing. In view of potential toxic and environmental risks for users and patients, a careful risk-benefit assessment must be conducted for each newly developed product impregnated or coated with antimicrobial agents, prior to marketing and manufacture.It has been proposed that incorporation of silver threads into the clothing of emergency service workers could reduce microbial contamination over time. As clothing in the emergency services is often not adequately changed, and it is plausible that microbial contamination increases with time in use, a study was conducted in the emergency medical setting in order to test this hypothesis. We compared the contamination rates of newly developed silver-hybrid clothing with that of standard textile clothing. Samples were taken from jackets and pants of 10 emergency workers at day 0 (pre-service), day 3 and day 7 after use over a divided 4-week period to examine this hypothesis. No significant difference in the extent of microbial contamination was detected between these two materials. A larger sample size is required to further verify this result.

Introduction

The incorporation of antimicrobials into everyday products, such as the coating or impregnation of surfaces in refrigerators and food-storage containers to prevent mold infestation or bacterial decay, the antibacterial impregnation of sport socks to avoid odor, or weaving silver threads into textiles as a supportive treatment of atopic dermatitis [1], is increasing. Similarly, antimicrobial impregnation of surfaces, textiles, and clothing in the hospital is increasingly advertised as being able to prevent infection through their antibacterial properties. Using antimicrobial compounds, however, is not only associated with the potential antimicrobial effect, but is also associated with potential risks, such as selection of microorganisms, environmental issues, and potential toxicological and allergic side effects. Therefore, a careful risk-benefit assessment for every product, including assessment of the users’ practical needs for antimicrobial impregnation or coating, is required, just as it is routinely performed for example for Class III medical devices [2]. A positive example for a beneficial antimicrobial medical device is the impregnation of surgical sutures with triclosan, the effectiveness of which has been demonstrated in not only in-vitro and animal studies, but in clinical use by measurable reduction in the rate of surgical site infection [3], [4].

The German Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung, BfR) has published the following recommendation for the use of nano-silver antimicrobial finishing: “The BfR recommends that manufacturers should not use nano-scale silver or nano-scale silver compounds in food and everyday products until adequate data is available, allowing a final health risk assessment to be performed, thus ensuring the safety of products. In order to adequately complete a scientific risk assessment, a study on the effects of silver cation and nano-silver material on antimicrobial resistance is urgently needed” [5].

Regardless of the potential health risk and the risk of developing bacterial resistance, the use of biocides should generally be avoided, especially if the same effect can be achieved using common hygienic or non-antimicrobial based measures [6]. This principle is important because biocides specifically for use in textiles may have side effects through direct body contact, such as sensitization with induction of allergies, change in the micro-ecology of the skin, development of resistance with possible cross-resistance to antibiotics, toxic long-term risks, and the development of eco-toxicological effects over time due to absent or poor biodegradability [3], [6]. The risk of microbial resistance development is of particular importance – a slow steady release of small amounts of silver ions may cause bacterial resistance. A transferable resistance to copper ions also used as an impregnated antimicrobial and cross-resistance to antibiotics has already been shown [6], [7]. A serious hazard has also been observed with the use of impregnated antimicrobial products, when the user disregards the usual proven measures of hygiene, such as washing textiles or cleaning surfaces, due to the ‘antimicrobial’ nature of the product.

A general principle applies in the use of biocides for antimicrobial impregnation: because of their antimicrobial efficacy, all biocides must undergo a risk-benefit analysis in terms of potential toxic effects on humans and the environment. The benefits of impregnation for the intended indication should be weighed against the potential risks [6]. This is valid not only for the consumer sector, but more importantly in the antimicrobial impregnation of medical devices as well as furniture and equipment in hospitals. The trust of staff in the antimicrobial properties of these products can lead to neglect in the primary prevention of nosocomial infections, that is, not conscientiously performing the multi-barrier strategies and concerted use of measures to prevent infection, such as personal hygiene practices. This is dangerous in light of the unproven efficacy of some antimicrobial materials for infection prophylaxis.

The example of impregnation of doorknobs with nano-crystalline oligodynamically acting metal ions illustrates the possible consequences of providing false security awareness. The ability of the impregnated doorknob to prevent infection is not documented, and the microbicidal action is largely unknown. Although there is a decrease of the number of microbes by the oligodynamic effect of released silver or copper ions on the surface, the significant effectiveness depends on the particular bacterial species, the present humidity, and the time of action. A significant microbicidal effect is occasionally exhibited at 3 hours, but typically takes between 6 and 9 hours. For doorknobs, clearly the time required to kill microbes is too long. For other products, time may play a different role, if, for instance, the contact times are far longer. This is the case for nano-silver impregnated vascular catheter material, as pathogens were no longer detected after 12 hours [7]. In sharp contrast to antimicrobial impregnation, decontamination of a doorknob is easily and immediately achievable through surface disinfection. If door handles are routinely disinfected, for example, twice a day with an alcohol-impregnated wipe, there is no doubt this will achieve a higher level of safety compared to decontamination through surface impregnation. Even more effective than disinfection, however, is non-contamination of surfaces such as doorknobs. Not the impregnated doorknob, the impregnated bed or even the impregnated hand basin will protect patients or staff from pathogens of nosocomial infections, but rather hand disinfection before each patient contact. This is the best evidence-based measure of infection prevention, which is supported by disinfection of the new patient’s surfaces, correct preparation of beds and medical devices, the rational use of antibiotics, compliance with hygiene standards in the daily routine of nurses and doctors, including the monitoring of pathogen spread through screening and surveillance. In other words, not the antimicrobial impregnation of surfaces in hospital is essential but the quality management of hygiene to protect patients from hospital infections.

The antimicrobial nano-technological impregnation of frequently used surfaces in hospitals is not only unnecessary in some indications and associated with high costs, but is also potentially dangerous. Besides the risks listed above, there are other reasons against antimicrobial coating or impregnation:

In case of protein impurities, the efficacy of silver and copper ions is completely negated [8].

Used on surfaces subject to mechanical stress, a reduction of the effective surface by abrasive removal of nano-particles is expected, i.e., the effect will literally wear off.

It is unclear whether nano-particles are released into the air through abrasion of the surfaces, a possibility which much be viewed critically in terms of toxicology. As long as this risk cannot be excluded, antimicrobial impregnation with nano-particles should be opposed for toxicological reasons.

In a nationwide analysis of health status in the emergency services in Germany [9], it was found that almost 10% of the staff of the sample in North Rhine-Westphalia changed their jacket only annually. In addition, 10% of the staff received only one or two personal work outfits (trousers, shirt, sweater, etc.), and only 75% of the ambulance stations had a general policy regarding the change of uniforms. Of these ambulance stations, 91% require daily change, and 80% request a change of clothing after contamination [9]. Based on these data, we decided to perform a study to determine the number of pathogens on these emergency workers’ uniforms. Five employees of the ambulance and patient transport company HKS Greifswald were asked to wear their uniforms for 5 d in service. Before the first shift and after the end of each working day, a sample from each of them was taken from the outside of the trousers’ left thigh and the polo shirt in the area of the breast pocket using Rodac blood agar plate (Rodac: Replicate organisms detecting and counting; heipha Dr. Müller GmbH, Eppelheim). These samples were subsequently incubated for 48 h and identified. For this study, the plates were placed obliquely and pressed for about 3 s to the respective surface. After 1 day, the pathogen load of trousers and shirt increased significantly and reached its maximum after 2 days (Figure 1 (Fig. 1)). Chiefly, representatives of the physiological skin flora (coagulase-negative staphylococci, M. luteus) were found, as well as S. aureus, Streptococcus spp. and ubiquitous spores which were not further differentiated. Based on this, we strongly recommend that the uniforms should be changed at least every two days (Figure 1 (Fig. 1)).

Figure 1

Contamination of uniforms (average of colony-forming units in 5 particular trousers) in 4 days of wear in the emergency rescue service

Instead of changing conventional uniforms every two days, an option would be wearing clothing incorporating silver threads, where a longer changing interval could potentially be considered. To compare these clothing types with respect to hygiene, an exploratory study was developed.

Methods

During the period from 11/01/2010 to 08/02/2010, the contamination of conventional ambulance service clothes (Güstrower Konfektions GmBH, Güstrow) was compared with that of SEE IT SAFE® Clothing (Niemoller and Abel, Gütersloh, Germany) in a cross-over study design.

Ten employees of an ambulance and patient transport company were selected to wear this clothing in daily service. In the first and third week, the conventional clothing was worn, with the staff wearing the SEE IT SAFE® clothing in the second and fourth weeks. The clothing was always worn by the same staff members. Before the start of the study and at the beginning of the week, the clothes were washed by the laundry of HKS with the same washing procedure. Afterwards, the clothing was sealed in plastic foil to prevent recontamination.

Before each first shift (pre-test value), and after completion of the third and seventh working day, contact samples were taken from each worker with Rodac blood-agar plate (size: 23 cm2) and incubated for 48 h at 37°C (98.6°F). The grown colonies were then counted and identified. The samples in each case were taken from the bottom of the right sleeve and the right and left front of the jacket as well as from the right thigh of the trousers, i.e., 4 samples per employee per day. The samples were taken after an interval of 1 hour after removal of the uniforms.

The number of colony forming units (CFU) found on the jackets was averaged for each day, separated into weekly results for the two weeks and then summarized. During the 4 weeks of this study, the average number of rescue operations done in one week only differed marginally. The average number of rescue operations of these 10 employees per day is summarized in Table 1 (Tab. 1).

Table 1

Average number of rescue operations of the 10 employees/d

Results

The first part of the study (weeks 1 and 2) showed that the concentration of the bacteria on the SEE IT SAFE® clothing was higher than on the conventional clothing, especially after the third working day (Figure 2 (Fig. 2), Figure 3 (Fig. 3)). Between the 3rd and 7th day, the CFU count was clearly reduced on the SEE IT SAFE® jacket and trousers, while the CFU count increased on the conventional trousers. The number of CFU on the conventional jacket did not differ after 3 d and 7 d (Figure 2 (Fig. 2), Figure 3 (Fig. 3)). An example of a sample of the SEE IT SAFE® jacket after 3 days of wear is shown in Figure 4 (Fig. 4).

Figure 2

Average number of CFU on the jacket in the first part (n=15/day/type of clothing) of the study

Figure 3

Average number of CFU on the trousers in the first part (n=5/d/kind of clothing) of the study

Figure 4

Contact culture on Rodac blood-agar from a SEE IT SAFE® jacket after 3 days of wear

The second part of the study (weeks 3 and 4) showed results similar to those of the first part with respect to the jackets, i.e., a significant increase in the number of CFU at the 3rd day, again with a larger number of CFU seen in SEE IT SAFE® jackets, but this time with a gradually increasing CFU until the 7th day (Figure 5 (Fig. 5)). Concerning the trousers, the course differs from the first part of the study. After 3 days, as in the first part, there was a significantly increased number of CFU in both conventional and SEE IT SAFE® trousers, but this time, a less pronounced difference in the SEE IT SAFE® clothing was observed. After 7 days, there was no difference between the two materials (Figure 5 (Fig. 5), Figure 6 (Fig. 6)).

Figure 5

Average number of CFU on the jackets in the second part (n=15/d/kind of clothing) of the study

Figure 6

Average number of CFU on the trousers in the second part (n=5/d/kind of clothing)

Overall, after concluding both parts of the study, it was shown that the number of CFU on the SEE IT SAFE® jackets, with the exception of day 0, was 3.8 times higher on day 3 and 2.3 times higher on the 7th day compared to conventional clothing (Figure 7 (Fig. 7)). Concerning SEE IT SAFE® trousers, the number of CFU at days 0 and 7 was lower than on conventional clothing. However, after 3 days, the number of CFU on SEE IT SAFE® trousers was nearly twice that on conventional clothing (Figure 8 (Fig. 8)).

Figure 7

Average number of CFU on the jackets in the whole study (n=30/d/kind of clothing)

Figure 8

Average number of CFU on the trousers in the whole study (n=10/d/kind of clothing)

The contamination of the sampling sites on the conventional clothing at days 3 and 7 was found to be significantly lower (p<0.001 and p<0.001, respectively) than on the silver textile (Table 2 (Tab. 2)). In contrast, there was no difference found in the contamination of the sample sites on the trousers (Table 2 (Tab. 2)).

Table 2

Results of the significance testing at conclusion of both parts of the study (Mann-Whitney U-test (2-sided))

Discussion

Considering only the investigated endpoints of the study after 7 days of wearing both types of textiles, the contamination of the SEE IT SAFE® jackets was higher. While this difference was considerable for jackets, there was no difference in trousers. The reason for this difference is unknown. The phenomenon, that over the course of 1 week the number of microorganisms on the trousers decreases again after an initial increase has been previously shown [9]. Since the sampling point on the trousers was twice as contaminated as the jacket (average of all values, Figure 7 (Fig. 7), Figure 8 (Fig. 8)), it might be possible that the effect of silver is only shown at a higher contamination level.

Although for jackets the microbial counts were higher and there was no difference for trousers, fundamentally, there was no hygienic advantage to SEE IT SAFE® clothing. Yet, the obtained results are not entirely surprising. In the analysis of atopic dermatitis patients wearing silver undergarments, we found a reduction of S. aureus of only 0.5 log, and determined a total colony count reduction of 0.4 log during the time of wearing. It should be noted that because of skin transpiration – in contrast to the relatively dry outside of the uniforms (winter without snow) – a better development of the effect of released silver ions is expected. After 2 days of wearing the placebo textile, the inside yielded 385.6±63.5 CFU and 236.5±49.9 CFU S. aureus, and 279.9±78.7 CFU and 119.3±39.4 CFU S. aureus were detectable on the silver textile. By daily washing at 60°C with conventional laundry detergent, contamination in both cases was almost completely eliminated [1].

When interpreting the results, it is important to note that the sample size of this study was not representative for a final assessment. Therefore, increasing the sample size should be considered for further evaluations.