We have now explored how to define a wound infection and how to identify a wound infection. What we now need to discuss is how to effectively diagnose a wound infection. We’ve already explored and described the covert and overt signs of a wound infection and the different terminology of contamination, colonisation, local infection, spreading infection, and systemic infection, and the signs and symptoms that go alongside them. But we know that characteristics of both the individual, their wound and the environment can contribute to the development of an infection in a wound. And the type of wound, be it acute or chronic, can contribute to the infection risk. So it’s essential that we’re able to identify early signs and symptoms.
In most cases, development of a wound infection is multifactorial and can occur when there’s a cumulative risk of factors that overwhelm the patient’s defence system. Infectious acute wounds tend to occur in otherwise healthy individuals. And actually, it’s quite easy to identify wound infection then, because the patient will complain of pain, malaise, feeling generally unwell and they will probably have a pyrexia. However, in immunocompromised individuals and those with chronic wounds early detection of infection relies on identification of the covert signs, which include a friable red granulated tissue, an increase in malodor, new pain or increased pain with a change in sensation, and delayed wound breakdown beyond the expectations you will be expecting.
It’s essential that clinicians act promptly if there any signs or symptoms of a wound infection, because we do not want it to turn into sepsis and risk of gangrene or necrotizing fasciitis. So the scoring systems can be used, such as asepsis, which has been validated for assessing surgical site infection of external wounds. And the Centre for Disease Control and Prevention have developed the definitions for wound infection. But they are limited surgical site infection. However, they are still useful to be aware of. These validated scoring systems can help to aid diagnosis or wound infection in chronic wounds.
Although not validated for chronic wounds, it is useful to transfer some of those signs and symptoms across to make people more aware of what they’re looking for. And again, we do have a range of investigations that can help diagnose a wound infection. These include your microbiological investigations, blood tests, and imaging. And these help to establish a specific pathogen within the wound bed. They can confirm the microbes that are sensitive to antibiotics that have either been commenced or to be prescribed. And they can identify any possible complications and help guide future management strategies. But these microbiological investigations depend upon the availability of local services.
So look around your own areas and see what your microbiological services have to offer, what they can and they cannot do. There may be some tests that you need to send off to an external agency to have them reported on. Similarly, microbiology shouldn’t be undertaken routinely or without substantial cause. So there are certain indications that you should consider when undertaking these microbiological tests, if you’ve got an acute wound that has classical signs and symptoms of infection, then you need to know which antibiotics need to be prescribed, if you’ve got a chronic wound with spreading or systemic infection. And again, this is the correct and appropriate use of antibiotics and antimicrobial wound dressings.
Sometimes we have infected wounds that you’ve been using antibiotics on for a period of time, and antimicrobials, and there’s been no change at all. So you’ll need to send off for more microbiological data to see what’s changed within that wound bed. And again, wounds where there’s a presence of certain species that would negate a surgical procedure, particularly important in patients who are going for skin grafting.
To better diagnose, there’s a range of diagnosis tools that you can use. We can use imaging tests, surgical procedures, and also wound swabbing.
You can see from this slide in front of you, this is a technique of a percutaneous bone biopsy of the foot. It won’t be used by every practitioner, but it’s worth knowing about. It can be carried out in the bedside or in the radiology suite or in the operating room. But it should be undertaken by an appropriate trained and experienced professional. But it’s worth being aware of these. Lipsky in his work with his team has identified a range of diagnostic techniques that I do encourage you to go and look at the papers that will be available in the resource section, as well, to look at. But we have talked quite a lot about biofilm.
We mentioned biofilm when we looked at the wound infection continuum. And we’ve talked about biofilm, to be aware of it when a wound maybe will not heal. But what is a biofilm and why is it important? And there have been significant advances in emerging science that helps us understand wound biofilms in the clinical context. However, biofilm-associated complications can increase the risk of morbidity and mortality. So we do all need to be aware of what is a biofilm. So it does go through a range of different stages. There’s a planktonic phase, where you have free-floating non-attached single microbes that attach to a surface or each other. In this early phase, the attachment is weak and reversible.
And most antimicrobial treatments can disrupt or kill these microbes when it’s in this planktonic phase. However, we can then have an irreversible attachment. And if these microbes are anchored together to a surface and they’re not separated, then these attachments and appendices become far stronger.
We then have cell proliferation, where after the attachments become strong and irreversible, microbe cells begin proliferating via a mechanism by which bacteria can regulate and respond to fluctuations in the cell population density. This process results in the formation of microcolonies. And then unfortunately, we have growth and maturation, where the biofilm grows and differentiates. And it culminates in a mature biofilm community, with structural features such as water channels and towering clusters of cells. The patient’s defences are then inadequate to eradicate the biofilm, but recognise its presence with inappropriate over recruitment of neutrophils and pro-inflammatory cytokines, and excessive host derived proteases. This then leads to tissue destruction and increased capillary permeability, which, in turn, provides nutrition for the biofilm.
And once a biofilm’s in its mature state, the normal wound management strategies become far less effective. So it’s essential that we’re able to identify a biofilm in a wound. To be able to identify this biofilm, we can use a range of different diagnostic techniques, such as scanning microscopy. Which James and his team in 2008 away established that 60% of chronic wounds contained a biofilm, compared to 6% of acute wounds.
And these biofilms do prevent the wounds from following their normal healing trajectory. And please be aware that biofilms cannot be seen by the naked eye. We cannot just look at a wound and say, there’s a biofilm there. What we can do is look at a wound and think, it hasn’t moved through the normal stages. And we can assume a biofilm is present.
The slide in front of you here shows some quite nice visuary examples of a biofilm within a wound. And they are linked to persistent human infections. And it is accepted that presence in chronic wounds may be linked of a failure to heal. So please take a few moments just to have a look at this slide and see exactly what biofilms can look like on a chronic wound bed.
As we spoke about earlier, a biofilm cannot be seen by the naked eye. However, when you’re undertaking your assessment, if there is a failure of appropriate antibiotic treatment to help kickstart the wound, or there’s a recurrence or delayed healing, there’s increased exudate or moisture, there’s a low level of chronic inflammation or a low level of erythema, you’ve got this friable tissue and there’s secondary signs of infection, then you can assume there is a biofilm present, and you will need to try and eradicate that biofilm.