One in 10 patients entering an acute hospital develops a health-care-associated infection, 9% of which are wound infections (DH, 2003). The annual cost of treating such infections puts an additional burden on limited NHS resources. This article discusses current thinking on dealing with infected wounds and highlights methods of preventing cross-infection.
Patricia Davies, BSc Hons, RGN, RM.
Senior Lecturer in Tissue Viability, University of Central England
Prevention is more cost-effective than attempts to cure (Nettleman, 2003). Not all infections are inevitable and taking precautions can greatly reduce incidence (DH, 2004).
The Department of Health (DH) has set targets for reducing bacteraemia caused by methicillin-resistant Staphylococcus aureus (MRSA) from 2005 in NHS acute trusts (DH, 2004). Surveillance of serious blood-borne infections, including MRSA, has been taking place since 2001, and last July the DH began to publish MRSA incidence rates in acute trusts, which will now be released annually.
To address the problem of hospital-acquired infections requires an improvement in infection control procedures. The DH (2004) acknowledges the need for a multidisciplinary approach. The main emphasis must be on preventing transmission and removing the sources of bacteria. For nurses, this involves:
- Cleaning: for example, cleaning equipment and following hand-hygiene guidelines
- Using protective barriers, such as wearing gloves and aprons
- Isolating patients
- Educating staff, patients and carers.
None of these practices is new. Essentially, they mark a return to basics, but with the difference that these activities are now based on evidence rather than performed ritualistically. However, they are effective only if they become second nature to practitioners and are seen to be high on our agenda. In wound-care management this means carefully considering our actions (see Questioning Practice box, p30).
The principles addressed by the questions listed in the box are important in both preventing wound infections and containing an infected wound to the host patient.
The document Winning Ways (DH, 2003) states that the use of aseptic technique is an integral part of infection control. Ward managers and senior staff need to ensure that new or agency staff are able to practise aseptic technique adequately.
What is an infected wound?
Wound infection is said to have occurred when there is a systemic response to an invading pathogen that is multiplying (Ayton, 1985).
Wounds are not usually sterile. Even under strict aseptic conditions it is difficult to ensure that a wound is completely sterile, as it is likely to be contaminated by the body’s natural skin flora. Wound cleansing in theatre is an attempt to reduce skin flora to a minimum to prevent introducing pathogens. The use of occlusive or waterproof dressings after suturing helps to protect a wound from infection until it seals itself, which usually occurs within 24-48 hours.
In some wounds, pathogens may be said to be colonising the wound - this means that they have settled and are reproducing in the wound, but are not affecting the host (Ayton, 1985).
In recent years, the notion of critical colonisation has been discussed (Kingsley, 2001). This is where colonisation is increasing and the bacteria are competing with the host for nutrients; it leads to the release of toxins that begin to have a localised effect, demonstrated by delayed healing.
Critical colonisation is considered to be detrimental to wound healing and it can be treated with topical antimicrobials. This course of action aims to prevent progression to an infected state, which would necessitate management with systemic antibiotics (Kingsley, 2001).
Detecting wound infection
To determine whether a wound is infected, a holistic assessment is required, including a detailed examination of the wound and the surrounding area. There are many indications of an infected wound (see Symptoms box, below).
Cutting and Harding (1994) propose that additional factors must be addressed in considering whether a wound is infected. This involves asking the following questions:
- Is there a delay in healing or is the wound breaking down further?
- Is there fragile granulation tissue, which bleeds easily?
- Is there bridging of soft tissue or pocketing at the base of the wound?
- Is the wound discoloured?
It is important to assess the clinical signs of infection and not to rely solely on laboratory results from a wound swab. All wounds contain some pathogens, and laboratory detection alone could result in the unnecessary use of antibiotics. A wound swab should be taken only if a wound is determined to be clinically infected, and not merely ‘to see’ if it is infected.
The exceptions to this are patients with diabetic foot infections or those who are immunocompromised. These groups are at greater risk of infection (Falanga, 2001): such patients have a diminished immunological response, which means that they may fail to display classical signs of infection in the early stages.
Screening for infection
The test results from a wound swab are not the exact science we sometimes believe them to be, since the tip of the swab collects only the organisms it comes into direct contact with. In many cases, this involves just the pathogens on the wound surface, so that organisms deeper in the underlying tissues may not be detected (Scanlon, 2003).
There has been much debate on how best to take a wound swab - for example, whether to wipe across the wound or zig-zag; whether the tips of the swab should be wet or dry; and so on (Gilchrist, 1996). If as much of the surface as possible has been covered by the swab and there is a good covering of exudate, most surface organisms may be picked up.
Wound swabs should be used dry - the fluid from the wound will be adequate to produce a sample. If a wound is dry, practitioners should question the need to take a swab. However, in cases where screening for MRSA is necessary, swabs may need to be dampened because the wound may not be producing exudate. It is advisable to consult your local infection control guidelines for details.
If there is a large quantity of exudate, a sample aspirated from the wound into a plain, sterile specimen pot could produce a better result. Another option is to take a tissue biopsy, but this is not common practice in the UK, as not all clinical areas have the staff trained to undertake this procedure (Collier, 2004).
Traditionally, a wound is classified as infected if it contains more than 105 organisms per gram of tissue (Kingsley, 2001).
The relevance of this quantity to diagnose infection has been questioned by Bowler (2003), who suggests that rather than just looking at the quantity of the various bacteria, we need also to look at the interaction of bacteria with each other and the wound in determining treatment.
This concept is further explored when considering the synergistic activity within biofilms, which are communities of bacteria that produce and exist within a protective membrane, making them resistant to some antibiotics (Percival and Bowler, 2004). The work around biofilms is an emerging field in the context of wound care, and more work needs to be done to enable a better understanding of these interactive molecular processes (Percival and Bowler, 2004). However, until new methods are devised, we have to rely on traditional methods of counting individual bacteria.
Translating results into treatment
When a wound is diagnosed as being clinically infected, treatment with systemic antibiotics and appropriate wound care should be started without delay (Kingsley, 2001). If the diagnosis is based on clinical observations, it is not appropriate to wait 48-72 hours for the test results of a wound swab. The infection may worsen in the time required to identify the organism and obtain sensitivity results.
The choice of antibiotic usually depends on the flora present in the area surrounding the wound, wound type and local prevalence. The DH (2003) is encouraging a shift away from the use of broad-spectrum antibiotics to specific antibiotics in a bid to reduce further bacterial resistance. This could prove difficult in wound management, as there are many causative micro-organisms. The prescribing clinician and the microbiologist should discuss treatment options.
Wound management can be enhanced by the use of topical antimicrobials, as they can reduce bacterial counts at the wound bed and within the wound fluid, thus working in synergy with antibiotics. Antimicrobials have been reappearing in the past few years in response to antibiotic-resistant strains of bacteria. Opinion and practice is shifting towards using the less toxic, newer antimicrobials to reduce bacterial counts at the wound bed (Falanga, 2001).
When using antimicrobials it is important to understand their mode of action and, in particular, potential interactions with other drugs.
Silver content New products have been developed and some existing dressings modified to include silver (see box right).
Some dressings release silver ions into the wound, while in others the ions are locked into the dressing and act on the absorbed bacteria. In laboratory tests, the release of silver ions from dressings appears to have a better response than in vivo, so caution is need when extrapolating such findings to the clinical environment (Thomas and McCubbin, 2003).
Iodine preparations Iodine comes in two main forms, povidone iodine and cadexomer.
- Povidone iodine is available in many forms including powder, ointment, impregnated gauze swab dressing, spray and solution. The aqueous solution, not the alcoholic form, should be used to treat wounds
- Cadexomer iodine comes in dressing and ointment forms. It has an absorptive capacity and provides a sustained release over several days (Morgan, 2000). This form of iodine may be useful in treating infected exuding wounds because of its absorbent properties and prolonged antimicrobial action.
However, there is little clinical evidence to show which of the two forms of iodine is more effective. Iodine should be used with caution in patients with thyroid disorders and never in those with iodine sensitivity (Dealey, 1999).
- Honey preparations: The use of honey in wound care is not new - reports dating back to 1500BC refer to its use in the Ebers Papyrus (Root-Bernstein and Root-Bernstein, 2000). Manuka honey has proven effective in treating infected wounds, especially MRSA. However, there is an absence of evidence from randomised controlled trials (Molan, 2001).
- Antiseptics: Antiseptics have fallen out of favour in the past 20 years, but their use on grossly infected wounds is being reconsidered in the light of increasing bacterial resistance.
The relevance of the work on healthy tissue, which discredited their use, is also under question (Cooper, 2004). When considering the use of antiseptics the question should always be raised: is there any other product that would be as effective but less toxic? If the answer is ‘no’, then the use of antiseptics may be justified. However, they should always be used with caution, with the endpoint of treatment predetermined and the surrounding tissue protected.
- Maggots: Maggots are used for two purposes - to debride necrotic tissue and to eliminate bacteria from the wound. They achieve the latter by altering the pH of the wound fluid to a rate bacteria find unacceptable, secreting an antimicrobial substance and, finally, eliminating bacteria when the maggot ingests the wound fluid and tissue, as the material passes through its gut (Thomas et al, 2002). Care must be taken in heavily exuding wounds as the maggots may drown in the fluid. Frequent changes of secondary dressings can prevent this.
- Essential oils: Lavender, tea tree and ocimum oils, among others, are being examined for use in wound care (Orafidiya et al, 2003). While their use has been found to have some positive effects, they are classed as aromatherapy products and, until they are available on the Drug Tariff, only qualified aromatherapists are permitted to use them.
The management of infected wounds needs to incorporate more treatment options than antibiotics only. Topical preparations and the judicious use of antibiotics is necessary.
Preventing cross-infection is the key to reducing wound infections, and it is vital to educate staff and patients about the modes of transmission and prevention techniques. A return to older, but reformulated wound management preparations, such as iodine, silver, honey and maggots should be considered.
Department of Health guidance sets out criteria for trusts to monitor and implement preventive measures to tackle health-care-associated infections
- Regular, holistic wound assessment is necessary to develop and evaluate a wound-management plan
- Diagnosis of infection must be based on clinical signs
- Taking wound swabs in the absence of any clinical signs of infection is not justified, except in patients with diabetes or poor immune systems whose inflammatory response may be diminished
- Non-infected wounds containing methicillin-resistant Staphylococcus aureus should be treated as per local infection control guidelines, the aim being to heal the wound
- Patient education is necessary to ensure the patient is not unwittingly transferring bacteria from one part of his or her body to another
- Clinically infected wounds should be treated with specific narrow-range rather than broad-spectrum antibiotics
- Consideration should be given to the use of topical antimicrobial agents to reduce the risk of infection in high-risk groups
Source: Winning Ways - Working Together to Reduce Healthcare Associated Infection in England (DH, 2003)
- Do we have trolleys dedicated for wound dressings?
- Do we have enough wound-care packs?
- Do we take into a room/cubicle only the equipment/dressings necessary for a particular dressing change?
- Do we have the equipment to enable fluids to be warmed before cleansing wounds?
- Do we change every wound dressing before or just as strike-through occurs?
- Do we always understand the nature of the dressing materials we are using and their purpose, or is it a question of what is available?
- Do we wash our hands?
- Do we educate patients on how to prevent them infecting their own wounds?
- Do we have enough appropriately trained staff to carry out the work?
A VARIETY OF DRESSINGS HAVE BEEN MODIFIED TO CONTAIN SILVER
- NON-ADHERENT DRESSINGS.
Author’s contact details
Patricia Davies, Senior Lecturer in Tissue Viability, School of Primary Health Care, University of Central England, Westbourne Road, Birmingham B15 3TN. Email: firstname.lastname@example.org
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