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Reservoir bugs: sources of hospital-acquired infection

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VOL: 97, ISSUE: 46, PAGE NO: 54

Mandy Roberts, RN, DipHE, is a staff nurse, intensive care unit, Royal Cornwall Hospital, Truro

Hospital-acquired infections (HAIs) - also known as nosocomial or iatrogenic infections - occur in about 9% of in-patients, which amounts to at least 100,000 infections a year. These infections may be costing taxpayers as much as £1,000m every year (National Audit Office, 2000).

For some particularly vulnerable patients the result of such an infection may be catastrophic (Nicholson et al, 1997). Martin (1993) states that, during a stay in an intensive care unit, mortality is in part dependent on whether the patient succumbs to hospital-acquired infection (HAI). Warnick (1997) states that nurses are the mainstay of prevention and treatment and play a leading role in educating other members of the multidisciplinary team.

What is hospital-acquired infection?

As the name implies, HAIs are caused by organisms including, but not limited to, bacteria or viruses that colonise or infect the patient following admission to hospital (Brunner and Suddarth, 1993). Boden (1999) has defined HAI as occurring within 72 hours of admission.

The National Audit Office (2000) report is a sobering reminder to all health care workers of the real but often unrecognised implications of HAIs. It concludes that infection control needs to be higher on the agenda for all hospitals.

With the advent of antibiotic-resistant strains of some pathogens the goal posts for hospital infection control departments across the globe have moved. Molyneux and Chadwick (1997) note the increasing incidence of vancomycin-resistant enterococcus (VRE) and comment on the particular vulnerability of some patient groups, such as the immunosuppressed.

Morgan et al (2000) studied the incidence of methicillin-resistant Staphylococcus Aureus (MRSA) in men and women in Wales and found that it was most often isolated from swabs taken from males aged 75 and over (who are also potentially frail and vulnerable). Most of these positive samples came from patients with a history of hospital admissions.

Moellering (1998) notes that if VRE managed to transpose its genetic resistance the resultant pathogens would be terrifying. Even more worryingly, Petignat et al (1998) found that many patients actually infected with these organisms remain undetected because they are asymptomatic or have an infection with a long incubation period, or specimens are difficult to obtain. McFarland et al (1989) found that 63% of patients with positive rectal cultures for Clostridium difficile had no symptoms.

Vectors of transmission

In order to fully understand how infection is transmitted, it is necessary to look briefly at the chain of infection (Fig 1). Brunner and Suddarth (1993) say this chain as essential for the continued proliferation of an infectious disease or organism.

Literature review

Rotter (1984), Nicholson (1997) and Mikos-Schild (1998) all advocate good hand-washing technique as the single most effective infection control measure. Brunner and Suddarth (1993) have described the hands of the health care worker as the mode of transmission for pathogens. The reason for good hand-washing is to effectively render the hands free of these pathogens (Rotter, 1984). However, the literature also cites other sources of infection, such as contaminated equipment and surfaces. In these often forgotten reservoirs, organisms can happily survive for long periods, even though they are away from the optimal warmth and humidity of the human body (Hinchliff et al, 1991).

Byers et al (1998) found that, following routine terminal disinfection, 16% of room surfaces were still colonised with VRE. McFarland et al (1989) found that the hands of 59% of hospital personnel caring for patients infected with Clostridium difficile became contaminated; in addition, hospital rooms occupied by symptomatic and asymptomatic patients were found to be contaminated in 49% and 29% of cases respectively. Having taken rectal swabs from some 428 patients over a period of 11 months, McFarland et al also found that 21% of those patients with negative swabs on admission to hospital acquired Clostridium difficile during their stay in hospital.

Blythe et al (1998) studied environmental contamination with MRSA in their hospital. Following routine cleaning there was still heavy contamination of mattresses and pillows, with slightly lower rates of contamination on bedside lockers, nurse call bells and a commode. They advocate periodical audit of terminal cleaning as one way of reducing environmental reservoirs of infection.

Similarly, Dharan et al (1999) attempted to reduce the incidence of cross infection from the environment to patients via contaminated equipment. They found that bacterial counts were reduced only by twice-daily cleaning, rather than daily cleaning with disinfectant. However, this was found to be unachievable due to staffing levels and workload.

Brunner and Suddarth (1993) describe hospital cleaning as a specialised process which is very different to the way individuals may clean their own home. It is important during hospital cleaning that dust and dirt are not simply moved from one place to another with the emphasis on how surfaces appear, but that soiling is completely and effectively removed.

Dancer (1999) looked at the common micro-organisms associated with infections acquired in the hospital environment. He found there were few studies to demonstrate the efficacy of domestic services in UK hospitals and that hospital cleaning was a forgotten element of infection control. It was suggested that hygiene standards are budget-driven, and services in many hospitals had been contracted out to the lowest bidder.

According to Dancer, this contracting out has resulted in diminishing standards and that ultimately this is a false economy. Dancer believes that setting high standards of cleaning is a realistic and achievable outcome, while good hand-washing and sensible antibiotic prescribing is not.

Boden (1999) cites the use of moving and handling equipment as a potential source of infection when such items, having been contaminated by one patient, are then not properly cleaned before being taken to the next. Barnett et al (1999) also cite inadequate cleaning of manual handling equipment used by multiple patients as being the reason for colonisation of the devices with MRSA and Clostridium difficile. Martin (1993) states that it is vital to put strategies into place to reduce colonisation of medical devices.

Other equipment found to have been reservoirs for infectious organisms include electronic ear-probe thermometers. Porwancher et al (1997) conclude that, in a case where VRE was spread among seven patients, the same strain of the bacterium was isolated from the handle of an electronic ear-probe thermometer which had been shared between patients. The patients had been colonised or infected in separate units of the same hospital where the equipment was shared but personnel were not, suggesting that the outbreak had an environmental origin.

Weinstein et al (1976) traced a source of nosocomial bacteraemia to contaminated pressure-monitoring devices, while Oldman (1987) found that the of swabbing of nurses’ scissors yielded pathogens in 96% of cases.

Jones et al (1995) studied the contamination of stethoscopes used by personnel in an A&E department. They observed 150 health care professionals and found that 48% cleaned their stethoscopes daily or weekly, 37% cleaned theirs monthly, 7% cleaned theirs yearly, while a further 7% never cleaned them. Use of an alcohol swab was the primary method used for disinfection.

Eighty-nine per cent of the stethoscopes grew staphylococci; 19% yielded Staphylococcus aureus. The physicians’ stethoscopes had the highest bacterial count. Cleaning the stethoscopes with an alcohol swab reduced the bacterial count by 94%.

The National Audit Office (2000) noted that more than 25% of NHS trusts had no written policies for the use of devices implicated in the spread of nosocomial infections.

Noble et al (1998) investigated a case in which an elderly hospital patient was infected with and subsequently died from a strain of VRE that was traced to the toilet of a former patient (also VRE-positive). The toilet had overflowed and contaminated equipment in the new patient’s room. Swab results of the original patient’s room after terminal cleaning yielded positive results from many environmental surfaces, including the mattress, pillows, call bell, commode, door knobs, bedside chairs, table and sink (Noble et al, 1998).

Mostafa and Chackett (1976) tested the cleanliness of steel and polypropylene bedpans following disinfection by automatic and semi-automatic bedpan washers. They concluded that poor maintenance of bedpan washers also contributed to inadequate standards of cleanliness.


While the importance of hand-washing has been well documented, the widespread contamination of equipment and room surfaces in hospitals does merit further research. This would seem especially prudent in the light of the National Audit Office’s (2000) findings. Warnick (1997) notes that VRE remains in the environment for up to seven days, making its transference hard to prevent.

All hospital staff should be given increased education on infection control procedures as part of the compulsory yearly updates on fire training and basic life support. While all personnel who have close patient contact must strictly adhere to the principles of universal precautions, health care workers must not forget the importance of properly cleaning equipment.

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