Chronic Wound Infection

Make the Diagnosis: Infection of Chronic Wounds

Prior Probability

Chronic wounds are those that have not undergone an orderly healing process. This imprecise definition requires judgment about when a wound has become chronic. Not all chronic wounds are infected. Among patients with chronic wounds evaluated in the highest-quality clinical studies, the prevalence of infected wounds was 45% (95% CI, 32%-58%). Because of the heterogeneity (I²=82%) that is seen through the broad CI, a useful way to remember this is that about half of chronic wounds will be infected, with a range of about one-third to two-thirds.¹

Patients in Whom Chronic Wounds Should Be Considered Infected

The presence of a wound with delayed healing prompts a consideration for local factors and systemic factors that contribute to the delay. Infection of the chronic wound is a local factor that requires evaluation in all affected patients, independent of the presence or absence of classic signs such as purulent exudate, heat, edema, or erythema.

Assessing the Likelihood of a Chronic Wound Infection

The accuracy of the symptoms and signs of infection in chronic wounds has been poorly evaluated, with no finding assessed in more than 2 studies. Increasing pain from the chronic wound is the only finding that has shown a likelihood ratio (LR) CI that excluded 1.0 in each of the 2 studies (LR range, 11-20; see Table 85-1), though the absence of increasing pain is less useful (LR range, 0.64-0.88).^{2, 3} None of the classic findings of infection (ie, purulent exudate, heat, edema, or erythema) specifically identify infection in chronic wounds (see Table 85-3). Data from 1 study suggest that a swab of the wound, using Levine technique, may be useful, but this requires confirmation (LR+ 6.3, 95% CI, 2.5-15; LR– 0.47, 95% CI, 0.31-0.73).⁴

Reference Standard Tests

The reference standard for the diagnosis of infection of a chronic wound is a deep tissue biopsy culture, which is an invasive procedure. Microbial loads greater than 10⁵ organisms per gram of wound tissue or any growth of β-hemolytic streptococci indicate infection in a chronic wound. A deep tissue biopsy culture can be performed in an outpatient setting. The presence of peripheral vascular disease in an affected extremity may represent a contraindication to performing the procedure. Prior to biopsy, the operator and consultant should discuss the need for testing specifically for aerobic, anaerobic, fungal, or mycobacterial organisms and alert the microbiology laboratory so that the specimen is appropriately obtained and processed.