The second component of wound bed preparation as defined by the T/DIME paradigm is treating the infection and or inflammation, the first step of that component is recognizing infection and how it differs from inflammation.  Obviously, the most important difference is the presence of enough microbes in the wound bed and periwound tissue that healing is drastically impaired.  All wounds have some contamination; however, it is the number of bacteria, the kind of bacteria, and the condition of the host that determines the presence of “infection” and whether the patient requires systemic antibiotics, topical antimicrobial dressings, or plain dressings. 

Terms defining the presence of bacteria on a wound bed are the following:

• Contamination – presence of non-replicating bacteria on the wound surface without any effect upon the wound healing process; plain dressings are adequate unless the patient is immunocompromised, in which case antimicrobial dressings may be helpful in reducing the bioburden.
• Colonization – presence of replicating bacteria attached to the wound surface with no harm to the host and no effect on the wound healing process; as above, antimicrobial dressings may be helpful in immunocompromised patients (according to the guidelines discussed below).
• Critical colonization – presence of replicating bacteria on the wound surface with sufficient numbers to visibly affect the wound healing process; antimicrobial dressings are definitely indicated.
• Infection – presence of replicating bacteria that have invaded the surrounding tissue with visible effects in the wound healing process and in the periwound tissue; in which case both systemic antibiotics and topical antimicrobial dressings are indicated.
• Sepsis – presence of replicating bacteria that produces a whole-body inflammatory state termed systemic inflammatory response syndrome (SIRS); signs or symptoms include fever, chills, tachycardia, hypotension, confusion, vomiting, acidosis, severe hyperglycemia, or azotemia) in which case IV antibiotics with bacteria-specificity are indicated.

Signs of infection are the following:

• Erythema – usually darker than the erythema seen in an inflammatory response, for instance around a surgical site; distinct borders or streaking away from the wound; in diabetic foot ulcers, erythema that extends >2 cm from the wound edge has a high correlation with infection.[i]
• Pain – usually described as deep and throbbing
• Edema – usually diffuse borders and localized to the wound site rather than full extremity edema observed with chronic venous insufficiency or lymphedema
• Heat – usually can be palpated as warm periwound skin; may be measured with an infrared skin thermometer; a difference of 3ᴼF is significant
• Purulence – defined as thick exudate that may or may not have an odor
• Malaise – patient complaint of feeling tired, lack of energy

Management of infection includes debridement of the infected tissue, which is done by sharp or surgical debridement, in conjunction with the appropriate antibiotics.  Selection of the topical antimicrobial is predicated on the amount of exudate, patient allergies, size of the wound, presence of tunneling and undermining, and availability.  Silver has become one of the most prevalent, frequently-used antimicrobial agents in recent years due to its broad spectrum efficacy, its ability to be incorporated into every delivery system (hydrogels, foams, hydrocolloids, negative pressure foams, collagen compounds), and its lack of bacterial-resistance.  Silver can, however, be cytotoxic to fibroblasts and keratinocytes when present in high concentrations (defined as >60 ppm). [ii]  After a comprehensive review of 59 studies, Khansa, et al. published the following strategies for the use of silver dressings in treating wounds with critical colonization or infection:

1. Silver sulfadiazine should not be used in open wounds or burns because of its high concentration and rapid absorption.
2. Dressings containing nano-crystalline silver are recommended during the first 2-3 weeks of treatment to decrease bacteria counts and to reduce odor, and are used in conjunction with sharp or surgical debridement.  Silver containing dressings should not be used long-term.
3. Silver sponges are useful in the early stages of negative pressure wound therapy (NPWT) because of their silver ion concentration of 20-40 ppm which is bactericidal but not cytotoxic.
4. There is no role for silver-containing dressings on clean wounds.  Use of the same only increases the cost of care with no improvement in outcomes.
5. Silver-containing dressings do not decrease the risk of infection when used over closed surgical incisions.  Incisional NPWT with plain polyurethane sponge lowers the risk of complications for high-risk closed surgical incisions.
6. Alternative topical agents (e.g. octenidine and polyhexanide) may be helpful, especially when used with installation NPWT.²

Other topical antimicrobials are discussed at length in the following reference:

Weir D, Brindle CT.  Wound dressings.  In Hamm R (Ed), Text and Atlas of Wound Diagnosis and Treatment: 2^nd edition.  New York: McGraw Hill Education.  2019, 373-418.  Available at https://accessphysiotherapy.mhmedical.com/book.aspx?bookid=1334. 

[i] Joseph WS, Lipsky BA. Medical therapy of diabetic foot infections.  Journal of Vascular Surgery.  2010;52(12S):67S-71S. 

[ii] Khansa I, Schoernbrunner AR, Kraft CT, Janis JE.  Silver in wound care – friend or foe?  A comprehensive review.  Plast Reconst Surg Glob Open. 2019;7:e2390;doi:10.1097/GOX.0000000000002390; Published online August 9,2019.  Accessed October 18, 2019.