Assessment of Wound Infection

Original Editor - Stacy Schiurring based on the course by Diane Merwarth

Top Contributors - Stacy Schiurring and Jess Bell

Introduction[edit | edit source]

According to the International Wound Infection Institute (IWII) Committee, "wound infection is the invasion of a wound by proliferating microorganisms to a level that invokes a local, spreading and/or systemic response in the host. Microorganisms multiply within the wound, developing a range of virulence factors to overcome the host defences leading to local tissue damage and impeding wound healing."[1]

The skin is the largest organ of the human body and is the outermost interface between the internal human system and the external environment. It is estimated that the human skin is on average 25 metres squared in size, with areas of overlapping changes in temperature, humidity, and skin pH. The skin is home to a multitude of bacteria, fungi, viruses, archaea, and mites. These microorganisms make up the skin's microbiota, and can have a more diverse population than the microbiota of the human gut.[2]

Under healthy skin conditions, the majority of the skin's microbiota behave as mutualistic organisms. They can inhibit the spread of opportunistic parasites employing various mechanisms, contribute to the education of the immune system and help maintain healthy skin barrier homeostasis.[3] Typically, the host's defences can destroy invading microbes. However, skin and wound infections are common. When the body cannot manage an infection, skilled interventions may be required to assist host defences in removing or destroying the invading microorganisms.

  • For an overview of wound healing, please read this article.
  • For a more in-depth review of factors which can affect wound healing, please read this article.
  • To learn more about the body's response to acute and chronic inflammation, please read this article.

Signs and Symptoms of a Wound Infection[edit | edit source]

There is abundant evidence in the literature on assessing wound infection and identifying signs and symptoms that can lead the wound care professional to confirm a developing infection.[4]

Signs and symptoms are abnormalities which can be an indication for a potential medical condition. Whereas a symptom is subjective, from the patient's point-of view, a sign is objective evidence of a disease which can be observed by others.[5]

The IWII Wound Infection Continuum (IWII-WIC)[edit | edit source]

The IWII-WIC is an assessment tool which provides a framework for wound care professionals to understand the impact microorganisms have on (1) the host, (2) the wound and on (3) wound healing. The five stages in the IWII-WIC increase in severity as the microbial presence increases and begins to affect the host and wound functioning.[1][4] The creation of the IWII-WIC included the elimination of the descriptive term critical colonisation for local infection.[4][6]

The IWII-WIC includes five conceptual stages:[1]

Table adapted from the IWII-WIC 2022 update[1]
Stages Clinical Observations/Signs and Symptoms Host Reactions

(least microbial burden)

  • Microoganisms are present within the wound but are not proliferating
  • No significant host reaction is evoked
  • No delay in healing is clinically observed
Host defences destroy microorganisms via phagocytosis
2 Colonisation
  • Microorganisms are present and undergoing limited proliferation
  • No significant host reaction is evoked
  • No delay in wound healing is clinically observed
  • Due to the protective function of the skin microbiome, all open wounds are colonised with microorganisms at the time of skin breakdown
  • Microorganisms that colonise a wound may also arise from exogenous sources or as a result of environmental exposure
3 Local infection
  • Microorganisms are present and undergoing proliferation
  • Host reaction is evoked which can include a delay in wound healing
  • Local infection is contained within the wound and the immediate periwound region (less than 2cm)
  • Local infection often initially presents as covert signs and symptoms which may not be immediately recognised as a sign of infection
  • As infection progresses, overt signs and symptoms become evident and are more recognisable as an indicator of wound infection

Please see next section for more information on covert and overt signs and symptoms of local infection.

4 Spreading infection

(also known as cellulitis)

  • Extending induration
  • Spreading erythema
  • Inflammation or erythema >2cm from wound edge
  • Crepitus
  • Wound breakdown/dehiscence
  • Lypmphagitis (swelling of lymph glades)
Spreading infection may involve deep tissue, muscle, fascia, organs or body cavities and result in more wide-spread signs and symptoms such as crepitis or lymphangitis

(greatest microbial burden)

Systemic infection
  • Malaise
  • Lethargy
  • Loss of appetite
  • Fever/pyrexia
  • Severe sepsis
  • Septic shock
  • Organ failure
  • Death
  • Invading microorganisms can spread throughout the body via the vascular or lymphatic systems, evoking a massive whole-body host response with fever[4]
  • Potential systemic inflammatory response syndrome (SIRS)[4]
  • Systemic inflammatory response can also be triggered by a local wound infection via other pathways, such as (1) the release of toxins or a (2) dysregulated immune system


The development of the list of signs and symptoms of covert (also known as secondary or subtle) infection was in relation to chronic and or nonhealing wounds, or patients who are immunocompromised. These criteria are applied to burn wound infections given that severe burn wounds cause an immunocompromised state. The information in: Wound Infection in Clinical Practice: Principles of Best Practice – International Wound Infection Institute: International Consensus Update 2022[1] has a slight variation from previous information provided in presentations and included in research and review articles, but does not necessarily negate this information.

To clarify:

  1. Pain as a symptom of infection pertains to both acute and chronic wounds. In the chronic wound population, the distinction is that pain may be the first or the ONLY symptom of infection noted until the infection reaches an extremely severe level.
  2. The presence of pain (new onset or worsening) is listed for both overt and covert infection[7]
  3. The presentation in the 2022 Update showing covert signs and symptoms as the first to be observed is correct in that this refers to chronic wounds. These are the first signs and symptoms to be seen; by the time that the overt signs and symptoms are noted in a chronic wound or with a patient who is immunocompromised, the infection has reached a critical level. This also applies to a patient with a severe burn injury, as they are considered to be immunocompromised.

For stage 3, aggressive wound care with standard of care for that particular wound, as well as topical antimicrobial agents are recommended. Aggressive wound care is considered more invasive, often involving debridement and removal a nonviable tissue down to a bleeding wound bed, to encourage rapid wound healing and closure.

For stage 4 and 5, continue aggressive wound care and wound cleansing; both topical and systemic antimicrobial agents are recommended.[4] As always, a wound care plan requires an interdisciplinary team including medical doctors with prescriptive and debridement abilities.

Signs and Symptoms of Local Infection[edit | edit source]

Covert signs and symptoms of local infection[edit | edit source]

According to the IWII-WIC, the concept of covert local wound infection is used to describe the clinical indicators primarily observed in the chronic wound before the wound exhibits overt signs and symptoms of local wound infection.[1]

Covert signs and symptoms (also known as secondary[4] or subtle[1] signs and symptoms) of local wound infection may not be immediately recognised as a sign of infection, but are important to assess and explore. There is a significant subset of the population for whom these symptoms may be masked due to a compromised immune system. This could be caused by (1) comorbidities such as diabetes or an autoimmune disorder, or (2) from side effects of treatments such as chemotherapy. A compromised immune system can prevent a patient from exhibiting the host response critical for identifying the onset of infection.[4]

Covert signs and symptoms include:

  1. An increase in pain from baseline[4]
  2. Epithelial bridging[1][4]
  3. Hypergranulation[1]
  4. Bleeding, friable granulation bed[1][4]
  5. Increased exudate[1]
  6. A deterioration in the visible appearance of the wound[4]
  7. Delayed wound healing[1][4]

Overt signs and symptoms[edit | edit source]

Overt signs and symptoms (also known as classic[4], classic cardinal[1], or frank[8] signs and symptoms) of local wound infection are more well-known and traditionally associated with local infections. They typically become evident and are more readily recognised as an indicator of wound infection.[4] However, symptoms may be masked in people with compromised immune systems and/or poor vascular perfusion.[1]

Overt signs and symptoms include:

  1. Induration[4] (firmness around the wound)
  2. Increased temperature: fever of the patient[4] and/or increased local warmth of the soft tissue around the wound[1][4]
  3. Oedema: either immediately around the wound or involving an entire extremity[1][4]
  4. Erythema: immediately around the wound or spreading beyond the wound.[1] Streaking is the phenomena where erythema follows an arterial pathway toward the heart.[4]
  5. Abnormal of lab values: including an elevated white blood cell count.[4] Please read this article for details about abnormal lab values.
  6. Purulent discharge[1][4]
  7. Wound breakdown and enlargement[1]
  8. New or increasing pain[1]
  9. Increased malodour[1]

Biofilm[edit | edit source]

A biofilm is a community of microbes with genetic diversity and variable gene expression with behaviours and defences that produce unique or chronic infections.[4]

Biofilms are commonly found in chronic wounds; studies have found between 60-80% of chronic wounds contain biofilms. They can also be found in acute wounds. The role these microbes play in the wound and the effect they have on impairing wound healing remains unclear. This understanding can be complicated by the presence of multiple different species of microorganism present in the wound at a time.

Biofilms can exist throughout the wound bed and wound dressings. They have been found embedded in slough, debris, necrotic and other tissues.[9] Biofilm microorganisms can also be found beneath the wound surface within the tissue extracellular matrix.[10]

Currently, there is no gold standard for wound sampling to identify biofilm.[1] It is not identifiable by standard lab tests; identification can only be made via electron microscopy or fluorescence.[4]

Criteria for potential biofilm in wound:

  • Failure of appropriate antibiotic treatment[1]
  • Recurrence of delayed healing upon cessation of antibiotic treatment[1]
  • A tolerance to antimicrobial agents[1][4]
  • A tolerance or resistance against the host immune response[4]
  • Delayed healing despite optimal wound care and management[1]
  • Increased wound exudate[1]
  • Low-level chronic inflammation[1]
  • Low-level erythema[1]
  • Poor granulation and/or friable hypergranulation[1][4]
  • Covert or secondary signs of infection[1][4]

Sample Collection[edit | edit source]

Biopsy[edit | edit source]

Wound biopsies are an important diagnostic component in the management of chronic wounds to monitor for potential malignancy or infection. Taking a wound biopsy often requires sampling at the wound edge and in the wound bed. It is also recommended to take wound biopsies for wounds that have not responded to treatment after 2–6 weeks.[11]

Biopsy techniques include:[12]

  1. Shave
  2. Saucerisation
  3. Curettage
  4. Snip
  5. Incisional
  6. Excisional

Semiquantitative swab culture[edit | edit source]

There is controversy over the effectiveness of performing a swab culture and if the results will represent the infection. However, there is research which shows a correlation between bacteria identified in a swab culture and the bacteria identified from a tissue sample, specifically a biopsy. A swab culture will not give the level of quantitative results as a biopsy. However, if done appropriately, the results will identify the microbes that need to be targeted with antimicrobial interventions.[4]

Benefits of performing a swab culture:[4]

  • Less invasive than a biopsy
  • Can be easily performed by the bedside clinician
  • Provides quicker results which allow more timely targeted antimicrobial interventions

Please view the following optional 7-minute video for a discussion of the steps of wound swab culture collection via the Levine and Z-technique, plus an overview of setup and documentation.


Resources[edit | edit source]

Clinical Resources:

Additional Recommended Reading:

References[edit | edit source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 Wounds International. Wound Infection In Clinical Practice: Principles of best practice. Available from: (accessed 26/11/2022).
  2. Boxberger M, Cenizo V, Cassir N, La Scola B. Challenges in exploring and manipulating the human skin microbiome. Microbiome. 2021 Dec;9(1):1-4.
  3. Roux PF, Oddos T, Stamatas G. Deciphering the Role of Skin Surface Microbiome in Skin Health: An Integrative Multiomics Approach Reveals Three Distinct Metabolite‒Microbe Clusters. Journal of Investigative Dermatology. 2022 Feb 1;142(2):469-79.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 4.29 4.30 Merwarth, D. Management of Burn Wounds. Assessment of Infection in Burn Injuries. Plus. 2022.
  5. Nature. Signs and symptoms. Available from: (accessed 26/11/2022).
  6. Haesler E, et al.  Clinical indicators of wound infection and biofilm: reaching international consensus.  J Wound Care, 2019; 28 (Sup 3b).
  7. Farhan N, Jeffery S. Diagnosing burn wounds infection: the practice gap & advances with MolecuLight bacterial imaging. Diagnostics. 2021 Feb 9;11(2):268.
  8. White RJ. Wound infection-associated pain. Journal of wound care. 2009 Jun;18(6):245-9.
  9. Vestby LK, Grønseth T, Simm R, Nesse LL. Bacterial biofilm and its role in the pathogenesis of disease. Antibiotics. 2020 Feb 3;9(2):59.
  10. Kirketerp‐Møller K, Stewart PS, Bjarnsholt T. The zone model: A conceptual model for understanding the microenvironment of chronic wound infection. Wound Repair and Regeneration. 2020 Sep;28(5):593-9.
  11. Panuncialman J, Hammerman S, Carson P, Falanga V. Wound edge biopsy sites in chronic wounds heal rapidly and do not result in delayed overall healing of the wounds. Wound repair and regeneration. 2010 Jan;18(1):21-5.
  12. Ponnarasu S, Schmieder GJ. Excisional Biopsy. InStatPearls [Internet] 2021 Sep 2. StatPearls Publishing.
  13. YouTube. Wound Culture | Wound swab for culture and sensitivity | How to collect wound culture. Available from: [last accessed 28/11/2022]