Introduction

Biomedical engineers and technicians handle a wide range of biomedical devices from the hospital when performing functional tests, calibration and repairs. The term ‘biomedical devices’ in this article, was used for devices that are normally serviced by biomedical service staff but are generally seen as low-risk (i.e. not contaminated with blood or body fluids). Biomedical devices are intimately used in patient care having close contact with both healthcare workers and patients, and are susceptible to being carriers of microorganisms.

While devices known to have contact with infectious patients are decontaminated before being serviced, no one was responsible for cleaning general biomedical devices in our facility; it was not the responsibility of nursing staff and the cleaning contractors were not permitted to handle biomedical devices.

Professional communications identified three biomedical service staff in Australia that required blood tests after needle-stick or screwdriver stabs, and a number with unknown cause: skin staphylococcus infections, tuberculosis and possible Legionnaires (prophylactic treatment taken).

Anecdotal evidence from biomedical staff showed they were concerned about the risk of occupationally-acquired infection from servicing biomedical devices, and if they could be putting patients treatment at risk by cross-contaminating biomedical devices when working on multiple units at the same time. A further concern of passing coughs and colds onto patients was discounted by infection control staff; community infections were wide-spread, low risk, and not containable.

In Australia, hospital-acquired infections affect up to 6% of patients [1]. Many microorganisms are dangerous to immune-compromised patients and those with easy access to the body via wounds and catheters. Staphylococcus aureus (golden staph) causes over 4500 cases of health care-related infections per year; about 2000 of these involve methicillin-resistant Staphylococcus aureus (MRSA) with a 35% mortality rate [2].

There is increasing belief that environmental surfaces play an important role in transmission of pathogens [3]. These environmental surfaces extend to biomedical devices that may not show visible signs of contamination [4]. Some pathogenic microorganisms are able to stay viable in dry conditions and on non-porous surfaces with no enrichment for many months [5, 6].

This review was conducted to investigate if microorganisms that persist on biomedical device surfaces provide an infection risk to biomedical staff when servicing biomedical devices.

Materials and methods

There is no literature that examines the infection risk to biomedical service staff in performing their daily activities. An indirect approach was used to examine the different aspects that will affect the risk of infection: (a) The presence of microorganisms on biomedical devices; (b) Persistence of microorganisms on dry surfaces; (c) Occupationally-acquired infections for biomedical service staff; (d) Patient infections caused by transmission of microorganisms from biomedical devices; (e) Effectiveness of cleaning agents for removal of microorganisms from biomedical devices; (f) Manufacturer recommendations on cleaning biomedical devices.

Systematic reviews of the literature were conducted for two parts: (a) to find studies that had observational evidence on the presence and identification of microorganisms on biomedical devices; and (d) for evidence of transmission of microorganisms from biomedical devices to patients.

The other areas of investigation used more general searches of Google, and grey matter. For the last item, manufacturer operator and service manuals for current biomedical devices in current use were surveyed.

The systematic review identified literature by multiple searches of PubMed with key phrases identified in Table 1 and Table 2. References of these papers were searched for other applicable papers.

Table 1 Search terms to find microorganisms on biomedical devices were formed by the specific biomedical device names in conjunction with the phrase: (“Equipment Contamination”[Mesh] OR “Fomites”[Mesh] OR “Disease Reservoirs”[MAJR])
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Table 2 Search terms for outbreaks with biomedical devices implicated
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Criteria for inclusion in both parts required the object under investigation to be a biomedical device published between 1990 and June 2010 in English full-text papers.

Quality of the papers was set by requiring the methods section to include laboratory techniques that described swabbing, plating, culturing and testing of specimens. Further criteria for part (a) were for a sample size of 30 or more devices and details of the number of devices with microorganism colonisation. For part (d) the criteria required that the outbreak isolates be traced back to a biomedical device.

Biomedical devices were defined as those devices routinely serviced by biomedical engineering staff. Computing input devices (keyboards and mice) in clinical locations were included even though they may not be under biomedical service arrangements as they have similar handling by healthcare workers to biomedical device keypads and controls. Devices were excluded from the review if they were expected to be contaminated with blood and body fluids during their normal use (e.g. catheters, dental waterlines, endoscopes, dialysis, operating theatre beds, bulb syringe irrigators, scissors, and respiratory devices) or were patient room fittings not serviced by biomedical staff (e.g. curtains, toilets, light switches, over-bed tables). For devices with a high level of skin contact, only blood pressure cuffs were included; excluded were ultrasound probes because of the added complication of gel use, and stethoscopes and radiographic plates as these are not usually serviced by biomedical staff.

Results

Microorganisms on medical devices

From 53 potential papers, 26 were found on biomedical devices and clinical computer input devices (Table 3). Papers were excluded for sample size <30 (5), identification of blood only (3), number of devices with microorganisms not provided (4), reviews (2), policy (1), environmental contamination (6), equipment no longer in use (1), contamination relating to accessories or use (3) or not relevant.

Table 3 Schematic review details for biomedical devices
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In the observational studies reviewed, 58% of devices were colonised, with 67% and 49% respectively for biomedical devices and clinical computing devices (Table 4). But this colonisation did not extend to computer servers in central areas of critical care units [7]. At least one pathogenic organism was identified on 13% of devices. A wide range of microorganisms were identified for biomedical devices (Table 5), and for clinical computing devices (Table 6).

Table 4 Microbial contamination of devices likely to be handled by biomedical engineers during service or with similar handling by healthcare workers
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Table 5 Biomedical devices (%) with microorganisms identified
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Table 6 Clinical computer input devices (%) with commonly identified microorganisms
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Persistence of microorganisms

Microorganisms, regardless of transmission method, can persist for many months, even on dry inanimate surfaces (Table 7). Exposure- and outbreak-associated rates of infection vary widely (Table 7) from the low rates of HIV (1 in 300) [8], to high rates for hepatitis B (1 in 3) [8] and influenza (almost 1 in 2 with low vaccination rates).

Table 7 Persistence of microorganisms on dry inanimate surfaces with rate of infection
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Occupational risk

Healthcare workers (generally defined as those with routine patient contact) are not classified as high risk occupations with 0.7 fatalities per 100,000 workers compared to agriculture, fishing and hunting 29.4, or mining 18.0 fatalities per 100,000 workers [9].

The biggest cause of occupational infections for all healthcare workers is from blood and body fluid transmitted infections (hepatitis B and C, and HIV) and airborne transmitted (tuberculosis) with the highest incidence occurring in nurses, physicians and laboratory technicians [10].

HIV world data to 2002 [11] show that of 106 documented occupational-acquired HIV cases, 56 were nurses, 17 were clinical lab workers and 14 were doctors. Biomedical service staff could have been within the three housekeeper/porter/maintenance cases, or the five other/unspecified health care workers.

In the UK (1996−2007) [8], of 3773 reported occupational exposures to blood or body fluids, the highest risk was for nurses 46%, or doctors and dentists 40%. Biomedical service staff were not itemised separately but may be included in the 8% professions allied to medicine (includes general technicians), the 2% for ancillary staff (porters, security and housekeeping) or the 5% with unknown occupations.

Patient infections from contaminated biomedical devices

The systematic review identified 13 papers (from a possible 84) that described patient outbreaks with microorganisms that could be traced to contaminated surfaces of, or dust within, biomedical devices.

Syringe pump contamination caused an outbreak of Astrovirus gastroenteritis [12]. A blood pressure cuff was the source of an Staphylococcus aureus contamination in a dermatology ward [13]. Neonatal incubators with moderate contamination were identified as the source of outbreaks of Serratia spp [14, 15] and vancomycin-resistant Enterococcus (VRE) [16].

Both rectal and ear probe thermometers were implicated in transmission of VRE directly from contaminated equipment to patients [17, 18] and in another setting a contaminated ECG lead was the source of a recurring outbreak [19]. Of particular interest was a 38 day gap with no patient use (in a Burns unit) of the ECG lead between a discharged patient and the next patient who developed a culture from the same source.

Acinetibacter baumannii outbreaks in intensive care units were due to extensive environmental contamination including surfaces of ventilators, infusion pumps, pulse oximeters, blood pressure cuffs and keyboard covers [20–23]; repeated outbreaks in another location were traced to dust contamination inside devices: a ventilator, a continuous veno-venous hemofiltration unit and an air-mattress warmer [24].

Effectiveness of cleaning agents

Alcohol (96% ethyl alcohol, propyl-based alcohol or 70% isopropyl alcohol or swabs) is the cleaning agent most often used in microbial studies investigating cleaning of biomedical devices. In a systematic review [25], 70% alcohol was shown to be successful at reducing organisms on biomedical devices (mean reduction 82.1% colony forming units). Isopropyl alcohol was shown to be effective at reducing microorganisms on keyboards [26, 27], handset and keypad of pumps (patient controlled analgesia and epidural) [28], otoscopes [29], pulse oximeter probes [30].

Quaternary ammonium compounds were effective on blood pressure cuffs (wiping or dipping) [31] and had sustained inactivation of pathogens on computer keyboards [26, 27] but microorganisms on keyboards could be removed equally well with four different disinfectants (containing chlorine, alcohol, phenol or quaternary ammonium) or sterile water (though the water did not inactivate difficult-to-treat VRE) [27].

Jones et al. [32]. extrapolated from hand washing guidelines to recommend 10 s of vigorous washing followed by a thorough rinse for stethoscopes, and Nunez et al. [33] used 10 s of rubbing to test cleaning agent effectiveness.

Manufacturer recommendations for cleaning biomedical devices

A survey of operator and service manuals for 81 devices from 56 manufacturers (38 device types) found 74% recommended water and detergent for cleaning. Only 53% recommended the use of alcohol. Bleach was recommended by 25% of manufacturers and ammonia by 7%.

Discussion

To make up for the lack of literature directly examining the infection risk to biomedical service staff in performing their daily activities, an indirect approach has been used to answer a range of questions that affect this risk. A systematic review was used to provide evidence for two parts of this analysis; the questions were simply framed and the papers that met the criteria were easily selected. Multiple reviewers were not used for screening of potential papers, or for assessing reviewer bias.

The systematic review has shown significant contamination of biomedical devices by a wide range of microorganisms, and that contaminated biomedical device surfaces and dust can be a source of patient outbreaks. General literature searches showed the microorganisms can persist for long periods on dry surfaces, however they are easily cleaned.

While the risk for patients is recognised and documented, occupationally acquired infections for biomedical staff are not reported. Health-care workers are at risk of infections from these microorganisms. Occupational risk after exposure is low for some of these infections, e.g. 1 in 300 for HIV, but the consequences can be severe. Biomedical engineers would be wise to consider the risk of occupationally-acquired infection and take appropriate actions to reduce this risk.

Visible signs of contamination

It is naive to think that microbial contamination is only present with visible signs such as blood. The risk of environmental surface contamination is confirmed by Hall [4] in finding 33% of surfaces in operating rooms (including monitor cables and pulse oximeter probes) contaminated with blood but only 2% with visible signs (three of 137 contaminated surfaces). Hall also draws attention to the problem of non-visible saliva contamination by which hepatitis B is transmitted.

Perry and Monaghan [34] took 336 samples from anaesthesia and monitoring equipment ready for use in 28 operating suites and found 37% were positive for occult blood, yet only six samples showed visible blood. Monaghan [35] also studied laryngoscopes finding no visible blood on 65 blades or handles yet occult blood on 30% of these.

Environmental cleaning

Some studies showed environmental cleaning had no effect on the rates of hospital-acquired infections [36, 37] and others showed it could reduce transmission of pathogens [5]. If only floors and room fittings are cleaned, and not items frequently touched by healthcare workers such as biomedical devices, the cleaning would have nominal effect. Dancer et al. [38] showed a decrease in hospital-acquired MRSA infections by enhanced cleaning with detergent wipes (Tuffie, Vernacare, Bolton, UK) of near-patient hand-touch sites (patient lockers, over bed tables, bed frames) including clinical equipment (patient hoist, infusion pump, blood pressure stand) 3 times/day, 5 days/week. Although there are no studies measuring the effect of biomedical service staff in spreading hospital-acquired infection, Dancer’s work shows near-patient hand-touch sites are important in the transfer of MRSA infection between patients.

Transmission from surface contamination

Only a handful of papers identified a biomedical device as the source of a patient outbreak; the major problems occurring with patients in high level care wards (ICU, NICU), or with poor skin protection (burns and dermatology wards).

Many studies have looked at the ability of microorganisms to transmit from a reservoir throughout an environment: keyboards in the operating rooms were found to be contaminated and microorganism could be spread from and to keyboards by wet contaminated gloves [26]; a surrogate marker of microbial transmission was spread from one telephone handset to five other neonatal intensive care unit pods over 7 days with a peak at 8 h with contamination of frequently touched places: blood gas analysers, computer mice, telephone handles, medical charts, radiant warmer control buttons, and patient monitors [39]; and badges showed little contamination difference between those involved in direct patient care (13.3%) and those not involved in patient care (14.3%), and no difference between clipped or hung around neck [40].

Cleaning agents for biomedical devices

The large number of publications that use alcohol in their test procedure to remove microorganisms is not in accordance with manufacturer recommendations which are mainly for detergent and water. One ultrasound manufacturer [41] with seven device types and 24 transducers provides a compatibility list of 112 cleaners and disinfectants; isopropyl alcohol (70%) is not one of those recommended.

Reprocessing of devices that contact intact skin only requires cleaning with detergent and water followed by drying [42]. Bleach is recommended for devices likely to contact body fluids (infusion pumps, defibrillators, thermometers etc.).

It is important to read the manufacturers recommendations for cleaning; they usually do not recommend abrasive cleaners, organic solvents, ammonia-based, acetone or alcohol-based solutions. Alcohol can dry out rubber seals and damage tubing [43] and is known to attack some forms of plastic, rubber, and coatings making them brittle [44]. If the device is visibly soiled alcohol should not be used without first cleaning with detergent and water, as alcohol can fix protein with the microorganisms to the surface being cleaned [45].

Infection control for biomedical staff

Biomedical engineering staff, like all other healthcare workers, should take infection control as a personal responsibility. Infection control practices include: standard precautions for contact with blood and body fluids common to all hospital staff, aseptic glove use, immunisations, and ongoing education about resistant bacteria and their spread.

The risk of occupationally-acquired infections in healthcare workers is documented for infections that are blood-borne and airborne, but not for those with indirect transmission paths [46].

While the biggest risk is to patients that are immune-compromised and have easy access of pathogens to the body via wounds and catheters, the risk of occupationally-acquired infections to biomedical service staff will increase with minor wounds occurring during service procedures, not covering minor skin breaks, and touching eyes and mouth with unwashed hands. This risk can easily be reduced by the use of alcohol hand rubs that should be available on all benches as compliance increases with easy access [47]; these are available with moisturisers and these have superior antimicrobial performance to soap and water [48].

Conclusion

The infection risk to biomedical staff when servicing biomedical devices has not previously been documented. This review draws together information that relates specifically to those involved in servicing biomedical devices. Biomedical engineers and technicians are at risk of being exposed to dangerous microorganisms from servicing biomedical devices. If they are healthy and without skin breakage this exposure is unlikely to cause illness.

It is recommended that biomedical staff follow good infection control practices, wipe devices with detergent, sterile water or alcohol swabs as recommended by the manufacturer before working on them, and keep alcohol hand rubs accessible at all benches.