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Soft tissue infections can affect the dermis, subcutaneous tissue, superficial or deep fascia, and muscles. Necrotizing bacterial dermohypodermitis (NBDH) is a necrotizing bacterial infection of the dermis and subcutaneous tissue which leaves the fascia intact, while necrotizing fasciitis (NF) affects the superficial fascia. By consensus, these two entities will be united under the term NBDH-NF in the remainder of the text [1-3].
These infections are serious but rare (500-1500 cases per year in the United States, no accurate data on the incidence in France) and carry a mortality rate ranging from 12 to 41% . Their management requires both surgical intervention and medical treatment, particularly antibiotic therapy. The clinician’s problem is to accurately diagnose NBDH-NF in a leg whose common initial presentation - swollen, hot, and red - suggests a non-necrotizing infection like erysipelas or bacterial dermohypodermitis. NBDH-NF can also affect the face, neck, chest, abdomen and perineum.
NBDH can be monomicrobial or polymicrobial. The most common causal pathogens in monomicrobial infections are group A Streptococcus pyogenes and methicillin-resistant Staphylococcus aureus, with an increasing incidence of community-acquired MRSA during the past decade, particularly in North America . Polymicrobial infections are caused by β-hemolytic streptococci, Staphylcoccus aureus, Gram-negative organisms and anaerobes (particularly after surgery or in patients with diabetes or a suppressed immune system). These infections usually originate at a point of bacterial inoculation, for example through a penetrating break in the skin, traumatic or otherwise, or a surgical incision. The bacteria proliferate locally in soft tissues (massive bacterial load), sometimes invading the fascia and muscles. Tissue necrosis develops as a result of several factors: cytotoxic and immunogenic effect of bacterial enzymes and toxins, extensive vascular microthromboses which may be accompanied by abnormal hemostasis with disseminated intravascular coagulation, and compression of the fascia by edema. In cases where there is no apparent inciting wound, the role of transient pharyngeal bacteremia has been suggested (chronic colonization by Streptococcus pyogenes).
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