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Are tympanic thermometers a source of cross-infection?

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VOL: 101, ISSUE: 19, PAGE NO: 62

Sarah Farnell, BSc, RGN, is research nurse practitioner, critical care, St George's Hospital NHS Trust, London

Aim: To find out if tympanic thermometers are a source of cross-infection in critical care and whether cleaning is effective.

Aim: To find out if tympanic thermometers are a source of cross-infection in critical care and whether cleaning is effective.

Method: An observational study.

Results: In most of the inspections the surfaces of the tympanic thermometers looked clean, but three inspections revealed spots of dried fluid and one revealed a dirty base. None of the swabs taken before or after cleaning was positive, but seven of the inspections identified that the lens of the tympanic thermometer was dirty, possibly with cerumen (earwax).

Conclusion: The findings from this study do not support the assumption that tympanic thermometers are a source of cross-infection in critical care, but a potential risk of cross-infection by this route cannot be excluded.

This study was instigated following an observation about the use of tympanic thermometers. It was noted that tympanic thermometers were not always cleaned in between patients and were therefore considered to be a cross-infection risk.

Literature review
Health care-associated infections namely MRSA and resistant coliforms are a huge problem within the NHS, especially within critical care. However, it has been suggested that about 30 per cent of health care-associated infections are preventable (Department of Health, 1995). In an attempt to prevent these infections, the Epic Project (Pratt et al, 2001) recommends that equipment used for more than one patient must be cleaned following each and every episode of use.

However, anecdotal and empirical evidence suggests that this does not always occur in practice. One study (Porwancher et al, 1997) discovered that the handle of an ear probe thermometer had been colonised by the same vancomycin-resistant enterococcus strain involved in clonal spread on a hospital ward. In this instance, the tympanic thermometer acted as a reservoir for the bacteria, which were carried to and from patients on the hands of the health care worker.

Although the main focus of cross-infection is related to that of poor handwashing compliance and technique, Conroy (2004) suggests that, 'other quite blatant modes of transmission are swept aside', such as the phlebotomist's tourniquet. Conroy observed phlebotomists and realised that they used the same tourniquet on all of the patients on all the wards throughout the hospital. To overcome this potential cross-infection route Conroy suggests that tourniquets should be disposable.

Bureau-Chalot et al (2004) demonstrated that blood-pressure cuffs, even after cleaning, could act as reservoirs for Acinetobacter baumannii.

Oie et al (2002) found that door handles in 53 (27 per cent) of the 196 rooms in a hospital were contaminated with methicillin-sensitive Staphylococcus aureus and/or MRSA. The latter was even detected on door handles in rooms where patients did not have MRSA. They suggest this may be caused by health care staff not complying with hand hygiene or contamination by other staff.

Health care workers' hands can contaminate many objects in the clinical area. One study has even identified that potentially pathogenic bacteria can be found on case notes (Bebbington et al, 2003). As a result, the authors recommend that handwashing should occur after handling case notes and before patient contact.

At the time of this study, four tympanic therm- ometers were shared among 16 patients in critical care. In view of previous research relating to cross-infection and shared equipment, it was believed that tympanic ear thermometers could act as a source of cross-infection.

This prospective observational study was undertaken in critical care between March and April 2002. Each of the four tympanic thermometers was swabbed randomly at three different sites. The handles were swabbed to detect potential hand contamination; below the earpiece was swabbed to detect potential contamination from the patient and the base was swabbed to detect potential contamination from environmental surfaces. To ensure a good uptake of the bacteria, the swabs were moistened with normal saline. The tympanic thermometers were also visually inspected prior to swabbing and any visible contamination documented.

The tympanic thermometers were then cleaned using detergent wipes and dried before the swabbing procedure was repeated. The rationale for swabbing after cleaning was to determine whether cleaning with detergent wipes was an effective decontamination method.

To ensure that the method of swabbing was consistent, and to prevent additional contamination, a protocol for swabbing was adhered to and data collection was undertaken by one researcher only. This inspection and data-collection process was repeated four times over a four-week period giving a total of 16 inspections. During this time, infection control data was collected to identify the number of patients with MRSA and/or resistant coliforms in critical care.

On most inspections (n=12), the surfaces of the tympanic thermometers looked clean. Three inspections revealed spots of dried fluid and one showed the base of a thermometer was dirty. It was also interesting to note that seven of the inspections revealed that the lens of the tympanic thermometer was dirty, possibly with cerumen (earwax). This suggests that in some instances a probe cover had not been used. This not only has implications for infection control but for the accuracy of temperature readings.

In order for tympanic thermometers to record an accurate temperature it is important that the lens is clean (Jevon and Jevon, 2001).

At the time of the swabbing, at least six patients were positive for MSRA and/or resistant coliforms. However, despite this none of the swabs taken before or after cleaning were positive.

The findings of this study do not support the assumption that tympanic thermometers are a source of cross-infection in critical care. However, due to the small nature of this study these findings are not conclusive and as such a potential cross-infection risk cannot be excluded.

Another possibility is that the swabbing might not have been effective at picking up any bacteria that were present on the surfaces. However, this seems unlikely because advice was sought from the infection control team regarding the swabbing technique before it was carried out.

If reliable, the negative results obtained from this study could be explained by the notion that bacteria require a moist environment in order to survive. However, this notion is disputed by Das et al (2002), who discovered that an outbreak of Acinetobacter was attributable to the curtains surrounding patients' beds. Therefore, dry objects in the environment can act as a reservoir for disseminating bacteria (Das et al, 2002; Porwancher et al, 1997).

Despite the lack of positive results produced by this study, some important issues have been highlighted. First, although on most inspections (n=12) the tympanic thermometers appeared to be clean, on some occasions (n=4) they were visibly contaminated with dirt or dried fluid.

This strengthens the argument for cleaning shared equipment between use on each patient (Pratt et al, 2001) and where possible, ensuring that separate equipment is set aside for infected patients (Porwancher et al, 1997).

Another issue highlighted by this study relates to the accuracy of the tympanic thermometer. Jevon and Jevon (2001) suggest that if the tympanic thermometer lens is not clean then its readings may be inaccurate. This study suggests that in seven out of the 16 inspections the lens of the thermometer was dirty. To ensure the device measures temperature accurately, staff should be encouraged to check the lens is clean prior to use. The lens should be gently wiped with dry gauze.

Another implication of the study relating to infection control was the suggestion that the dirt on the lens of the tympanic thermometer on one of the inspections may have been cerumen. It is important to ensure that a clean probe cover is always firmly attached to the tympanic thermometer prior to insertion into a patient's ear.

Although this study was unable to establish that tympanic thermometers are a source of cross-infection, the potential risk cannot be ruled out. As such, tympanic thermometers and all other shared equipment should be cleaned between patients (Pratt et al, 2001) and, where possible, separate equipment should be used on infected patients (Porwancher et al, 1997).

Furthermore, all staff who come into contact with patients and use equipment in the delivery of patient care should be aware of the need to decontaminate the equipment or environment between patient use and between procedures (Wiseman, 2004). This will help to reduce the risk of patients acquiring antibiotic-resistant infections.

With the increasing prevalence of health care-associated infections, and the subsequent human and financial implications, it is imperative that as health care professionals we constantly question our practice, identifying any concerns and making sure that they are addressed.

This article has been double-blind peer-reviewed.

For related articles on this subject and links to relevant websites see

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