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An evaluation of the infection control potential of a UV clinical podiatry unit
© Humphreys et al.; licensee BioMed Central Ltd. 2014
- Received: 30 August 2013
- Accepted: 19 February 2014
- Published: 28 February 2014
Infection control is a key issue in podiatry as it is in all forms of clinical practice. Airborne contamination may be particularly important in podiatry due to the generation of particulates during treatment. Consequently, technologies that prevent contamination in podiatry settings may have a useful role. The aims of this investigation were twofold, firstly to determine the ability of a UV cabinet to protect instruments from airborne contamination and secondly to determine its ability to remove microbes from contaminated surfaces and instruments.
A UV instrument cabinet was installed in a University podiatry suite. Impact samplers and standard microbiological techniques were used to determine the nature and extent of microbial airborne contamination. Sterile filters were used to determine the ability of the UV cabinet to protect exposed surfaces. Artificially contaminated instruments were used to determine the ability of the cabinet to remove microbial contamination.
Airborne bacterial contamination was dominated by Gram positive cocci including Staphylococcus aureus. Airborne fungal levels were much lower than those observed for bacteria. The UV cabinet significantly reduced (p < 0.05) the observed levels of airborne contamination. When challenged with contaminated instruments the cabinet was able to reduce microbial levels by between 60% to 100% with more complex instruments e.g. clippers, remaining contaminated.
Bacterial airborne contamination is a potential infection risk in podiatry settings due to the presence of S. aureus. The use of a UV instrument cabinet can reduce the risk of contamination by airborne microbes. The UV cabinet tested was unable to decontaminate instruments and as such could pose an infection risk if misused.
- Infection control
Infection control is a key issue in podiatry as it is in all forms of clinical practice [1, 2]. Infection control studies focussed on podiatry practices have demonstrated the importance of effective disinfection [3–5] and laundry processes [6, 7] in the reduction of environmental microbial contamination. This is important since environmental contamination is recognised as a source of healthcare associated infections (HAI) [8, 9] and a number of bacterial pathogens have significant survival times on inanimate surfaces . Airborne transmission is also potentially important , with pathogens such as Methicillin Resistant Staphylococcus aureus (MRSA) able to survive and be transported on skin scales . Airborne contamination is a particular issue in podiatry due to the generation of particulate materials during processes such as drilling [12, 13].
Bacterial infections associated with MRSA and Clostridium difficile have received considerable attention in the UK due to their dominant role in HAI [14–16]. In the podiatry setting, fungal contamination must also be considered due to dermatophyte infections, where onychomycosis can increase the risk of cellulitis, ulceration and subsequent infection to the elderly, immunocompromised and diabetic [17–19]. Dermatophyte infections are generally transmitted via direct contact with infected individuals, skin and hair debris or contaminated fomites . Fungi including dermatophytes have been shown to survive on laboratory equipment , healthcare surfaces , veterinary equipment , house dust  footwear and soft furnishings . In animal studies the airborne transmission of dermatophyte infections has also been observed .
Whilst steam sterilisation is the most common practice for instrument decontamination, it has been suggested that UV irradiation should be considered an adjunct to conventional cleaning and disinfection processes [27, 28]. Ultraviolet (UV) irradiation has broad spectrum biocidal activity with applications in air, surface and water disinfection [28–31]. UV disinfection has been specifically evaluated against fungi [30, 32, 33] and has received considerable attention as a treatment for airborne contamination in Healthcare settings [28, 34, 35]. However, its general use for space disinfection e.g. in operating theatres, has been curtailed by concerns over health risks [19, 36, 37].
UV podiatry cabinet
To determine levels of microbial air contamination within the Podiatry clinic impact samplers (MicroBio 2, Fred Parrett Ltd, UK) were employed sampling 400 litres of air at a sample rate of 100 l min-1. Air samples were taken before, during and after consultations. Bacterial samples were taken on Tryptone Soya Agar (TSA)(LabM Ltd, UK) and were incubated at 37°C for 24 hours; Sabouraud Dextrose agar with Chloramphenicol (SABC) was used for general fungal isolation with Dermasel agar (Oxoid LTD, UK) used to isolate dermatophytes. Fungal plates were incubated at 30°C for up to 6 weeks. In all cases colonies were sub-cultured for analysis.
In addition to air samples, sterile cellulose acetate filters (0.45 μm pore size, Whatman) were employed to determine the ability of the UV cabinet to prevent airborne contamination during routine podiatry consultations. Triplicate filters were placed in sterile Petri dishes located in both the UV cabinet and the standard instrument cabinet and exposed during routine podiatry consultations. After exposure the filters were placed on either TSA, SABC or Dermasel plates and incubated as specified for the air samples.
Disinfection potential of the UV cabinet
To determine the disinfection potential of the UV cabinet triplicate pre contaminated cellulose acetate filters were exposed to UV radiation from 1 to 30 minutes on two separate days. The filters were contaminated with either Staphylococcus epidermidis (NCIMB 12721), Aspergillus brasiliensis (ATCC 16404) (previously known as Aspergillus niger), Trichophyton tonsurans (NCPF 117) or Trichophyton rubrum (NCPF 5061). S. epidermidis was employed as a surrogate for pathogenic Staphylococci such as MRSA. The number of surviving organisms was determined as previously stated with the impact of the UV exposure calculated by comparison with sets of control filters.
S. epidermidis contaminated filters were prepared by filtering 0.1 ml of a 10-3 dilution of a suspension prepared as specified for Staphylococcus aureus in European bactericidal testing standards  giving a viable count of between 1.5×104 and 5×104 cfu filter -1. Trichophyton sp contaminated filters were prepared by filtering 0.1 ml of a test suspension containing 1.0×106 -2.0×106 spores ml-1 recovered from cultures grown on Dermasel plates and recovered as outlined in the European fungicidal testing standard .
Bacteria isolated during air sampling were characterised using a range of standard microbiological tests . Individual colonies were sub cultured into 96 well plates containing Tryptone Soya Broth (TSB)(Lab M Ltd). Following incubation at 37°C for 24 hours the 96 well plates were replicated onto a range of selective media using 96 well replicators (Sigma Aldrich Ltd) and 150 mm diameter plates. The media employed were chosen to allow the identification of MRSA, Staphylococcus aureus, other Staphylocuccus spp, Micrococcus spp and Gram negative bacilli. The media employed were TSA (aerobic and anaerobic incubation) Mannitol Salt Agar, Baird Parker Agar, Oxacillin Resistant Staphylococci Isolation Medium with methicillin supplement and MacConkeys Agar (all, Lab M Ltd). Presumptive MRSA and S. aureus isolates were confirmed via a coagulase latex agglutination test able to detect isolates possessing protein A and/or capsular 5 or 8 antigens. To further aid identification all isolates were Gram stained and tested for catalase and oxidase (both Prolab Diagnostics Ltd).
Fungal isolates recovered on SABC plates were sub cultured onto Malt Extract Agar and identified via microscopic examination. Isolates recovered on Dermasel plates were processed via a dermatophyte PCR kit (SSI, Denmark). PCR was carried out with primers encoding chitin synthase 1 (pan-dermatophytes) and Internal Transcribed Spacer 2 (ITS2) for the detection of Trichophyton rubrum. PCR product was run on a 2% agarose gel before being visualised under UV by ethidium bromide staining.
All statistical analysis was carried out using IBM SPSS V20.0.0 for Windows. Data were compared via Analysis of Variance (Anova) and a Tukey HSD post hoc test.
Average levels of airborne bacterial contamination (58.0 cfu m-3), were towards the lower end of the range published for a podiatry clinic prior to the application of a filtration system (79.0-117.0 cfu m-3), and slightly above those observed following the installation of a filtration unit designed for removal of chemical and microbial contaminants (26.0-57.0 cfu m-3) . With a wider scope, the numbers observed within the podiatry clinic fell between those published for empty (16.9 , 12.4  cfu m-3) and operational (140.1 , 93.8 , 123.2  cfu m-3) operating theatres. The levels were also below average values (116.0 to 165.0 cfu m-3) published by an extensive study of air conditioned office buildings in the USA. These levels are within the range published by the DoH for operating theatres, and below the maximum level expected in a working operating theatre . The relatively low average levels of airborne contamination experienced in the podiatry clinic may reflect the limited exposure to patient based activity in each cubicle when compared to busy hospital ward or out-patient clinical environments. Consultations carried out in the clinic studied required limited use of curtains, avoiding redistribution of contaminants by disturbing settled organisms as seen in previous studies, contributing to lower average values . There was no evidence that the levels of air contamination increased during consultations or that the length of consultation had an impact on contamination levels. This disagrees with previous studies  which have shown an increase in bacterial contamination with subsequent consultations, this difference is likely to reflect the improved ventilation employed in more modern podiatry clinics.
The dominance of the airborne microbiota by Gram positive bacteria, particularly cocci, is consistent with culture based [47–49] and molecular investigation [50, 51] of indoor [47–49] environments reflecting the human origin of many indoor, airborne bacteria [50–52]. The dominance of coagulase negative Staphylococcus and Micrococcus sp also agrees with observations from microbiological studies of podiatry cubicle curtains . The presence of coagulase positive Staphylococci, (presumptive S. aureus) albeit at significantly lower concentrations, indicates that airborne contamination does pose an infection risk. The risk posed by S. aureus in podiatry settings, particularly to diabetic and immunocompromised patients has been recognised by other authors . The same authors  also pointed out that the acquired infection rate associated with podiatry was considered to be “virtually nonexistent” although no supporting evidence was available.
The isolation of Aspergillus and Penicillium sp is also consistent with previous observations [47, 48]. The presence of very low numbers of airborne dermatophytes suggests that the risk of air transmission of fungal infections is low but does exist. It is more likely that the cross infection risk associated with dermatophyte infections is greater for contaminated instruments and fomites; this risk being controlled by the sterilisation procedures in place within the clinic for instrument processing.
Given the levels of airborne contamination it is not surprising that filters exposed without the protection of UV irradiation accumulated significantly more bacterial contamination than UV protected filters. The deposition rates are consistent with those associated with other healthcare environments being approximately 50% greater than floor level deposition data from working operating theatres (1790 cfu m-2 h-1)48. The presence of both pathogenic bacteria and fungi in the ambient air indicates that there is the potential for the contamination of sterile instruments placed in the standard sterile field employed by podiatrists. The data indicates that the use of a UV cabinet to store instruments prior to use, may reduce the chance of airborne contamination of instruments within the cabinet drawer and reduce any associated infection risk through patient contact with instruments. The UV cabinet may also remove any contamination due to aerial deposition between uses. However, UV exposure is unable to decontaminate instruments with significant contamination (>4 Log CFU/ml) due to the complex shapes of the instruments which prevent UV penetration. Equally, other decontamination methods have found issues with removing residual proteins from ultrasound and steam processed instruments . This suggests that the mis-use of the cabinet for the recycling of used instruments between patients may present a risk of infection through organism attachment to debris remaining on the instrument from previous disinfection processes . Given the lack of any substantiated data on podiatry associated infections within out-patient based clinic (where no surgery has taken place), it is likely that use of a UV cabinet could only be justified in the case of highly susceptible individuals. Where a cabinet such as this is available local procedure would have to be in place to ensure it is not misused i.e. not use to recycle instruments.
Darren Sandy of DLT Podiatry Supplies (Huddersfield, UK) provided the UV clinical unit on extended loan.
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