Wound infection is a serious complication of wound healing. Infection may be localised, spread into surrounding tissues and bone, or manifest systemically as sepsis, a life-threatening condition. Infection not only delays healing but patient recovery in general; it increases scarring, causes undue pain and suffering and leads to complications such as wound breakdown and/or dehiscence. The added costs to the health care system through increased length of stay or unplanned readmission to hospital is considerable. It is vitally important for health professionals to recognise the signs and symptoms of infection early to minimise the risk of spreading and ensure reparative processes progress along the healing continuum as they should.
Identifying wound infection

All wounds are contaminated with surface microorganisms, the presence of which does not imply infection. Progression from contamination to infection depends on several factors including the patient’s ability to fight infection, wound characteristics and microbial virulence. Patient factors in addition to the immune response to invading microorganisms, the type of microbes present in the wound bed and the capacity of microbes to adhere to the wound surface and replicate, as well as virulence, all influence infection. Co-morbidities such as diabetes, rheumatoid arthritis, cardiovascular and respiratory disease, and renal impairment; and patient factors such as age, nutritional status, obesity and smoking status impact healing, increasing patient susceptibility to infection. Similarly, medications that suppress immune system responses such as corticosteroids, immunosuppressants, chemotherapy and radiotherapy will increase the risk of infection and delay healing. Conditions that limit peripheral perfusion and the delivery of oxygen and nutrients to the wound, for example peripheral arterial disease, ischemia, wound oedema and exudate levels, create a wound environment that supports microbial colonisation. Dirty wounds with devitalised and necrotic tissue and unhealthy slough provide the conditions conducive for microbial adherence and replication; and biofilm formation.

Wounds will have various levels of microbial organisms which may or may not adversely affect wound healing. Contaminated and colonised wounds will generally heal without complications and it is important to remember that inflammation in the early stage of wound healing is normal and will continue for up to three days. Inflammation persisting beyond this time should be viewed with suspicion and be clinically reviewed. In critically colonised wounds, if not identified and treated in a timely manner, infection is imminent. Critically colonised wounds may show signs of non-healing, there may be changes to the type, colour, consistency, odour and amount of exudate, healthy granulation tissue (normally bright red, firm and shiny) becomes dark, dull and friable, the amount of devitalised tissue in the wound bed such as slough may increase or its appearance may change from a shiny, yellow, stringy consistency to a dull green/grey colour that is strongly adhered to the wound bed. The periwound and surrounding skin may show signs of inflammation (heat, redness, oedema, pain) with or without spreading erythema or the patient may feel generally unwell or become lethargic. 

Wounds that become infected can have serious and devastating consequences for the patient. Infection may spread into deeper tissues including bone resulting in osteomyelitis necessitating surgical intervention and/or amputation, or systemically which may become life threatening. Sepsis, a systemic inflammatory response to infection, is a severe complication resulting in organ failure conferring a high risk of mortality if not identified and treated early. Vigilance to signs and symptoms in the presence of a wound is necessary to avert such complications. In certain casesit should be assumed that the patient has sepsis until this is ruled out: an urgent clinical review is required if the patient is very young or is over 60 years of age and/or suddenly develops a temperature (greater than 38.5 degrees) with or without rigors or becomes hypothermic (less than 35 degrees), and/or is tachycardic (heart rate greater than 90 beats per minute) or tachypneic with a respiration rate greater than 20 breaths per minute, and/or their systolic blood pressure drops significantly (40 mm Hg) from the baseline or is less than 90 mm Hg, or their mean arterial pressure in less than 60 mm Hg, and/or their health deteriorates for no apparent reason. Blood pathology may identify a high or low white cell count with elevated CRP (C reactive protein) and lactate levels. Lactate levels greater than 4 mmol/L signify single or multi organ system failure and require immediate medical intervention.

Conclusion
Wound infection occurs as a result of an imbalance between patient characteristics, compromised immune responses to infection, wound characteristics and virulence of microorganisms present in the wound bed. Recognition of the more subtle signs of wound infection which often present at critical colonisation is an important and vital clinical skill that will ensure accurate and timely assessment and appropriate management. Additionally, the best clinical outcome for the patient can be ensured throughknowledge of patient characteristics and medications that may influence the patient’s susceptibility and capacity to fight infection, as well as systemic signs and symptoms of the systemic inflammatory response characterised by sepsis.