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Anaerobic Infections, Skin & Soft Tissue

For further information, see CMDT Part 35-31: Anaerobic Infections

KEY FEATURES

  • Several terms are used to classify these infections

    • Bacterial synergistic gangrene

    • Synergistic necrotizing cellulitis

    • Necrotizing fasciitis (see Necrotizing Fasciitis)

    • Non-clostridial crepitant cellulitis

  • Usually occur after trauma, ischemia, or surgery

  • Most common in areas contaminated by oral or fecal flora

  • May also be seen in persons who inject drugs or who sustain animal bites

  • All are mixed infections caused by aerobic and anaerobic organisms

  • Although there are some differences in microbiology among these infections, differentiation on clinical grounds alone is difficult

CLINICAL FINDINGS

  • There may be progressive tissue necrosis, evidence of gas in the tissues (crepitance) and a putrid odor

  • Pain out of proportion to the clinical findings

  • Hemodynamic instability and systemic toxicity may be present

DIAGNOSIS

  • Surgical exploration

TREATMENT

  • Broad-spectrum antibiotics active against both anaerobes and gram-positive and gram-negative aerobes (eg, intravenous vancomycin plus piperacillin-tazobactam with intravenous clindamycin for necrotizing fasciitis) should be instituted empirically and modified by culture results (Tables 32–5 and 32–1)

  • Antibiotics are given about a week after progressive tissue destruction has been controlled and the wound's margins remain free of inflammation

  • Aggressive surgical debridement of necrotic tissue is required for cure

Table 32–1.Examples of initial antimicrobial therapy for acutely ill, hospitalized adults pending identification of causative organism (listed in alphabetical order by suspected clinical diagnosis).
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Table 32–1. Examples of initial antimicrobial therapy for acutely ill, hospitalized adults pending identification of causative organism (listed in alphabetical order by suspected clinical diagnosis).
Suspected Clinical Diagnosis Likely Etiologic Diagnosis Medication of Choice
Brain abscess Mixed anaerobes, pneumococci, streptococci Ceftriaxone, 2 g intravenously every 12 hours plus metronidazole, 500 mg orally/intravenous every 8 hours, plus vancomycin, 15–20 mg/kg intravenously every 8–12 hours1
Endocarditis, acute (including injection drug user) Staphylococcus aureus, Enterococcus faecalis, viridans streptococci Vancomycin, 15–20 mg/kg/dose intravenously every 8-12 hours1
Fever in neutropenic patient receiving cancer chemotherapy S aureus, Pseudomonas, Klebsiella, Escherichia coli Cefepime, 2 g intravenously every 8 hours. If concerned for MRSA infection, add vancomycin 15–20 mg/kg intravenously every 8–12 hours1
Intra-abdominal sepsis (eg, postoperative, peritonitis, cholecystitis) Gram-negative bacteria, Bacteroides, anaerobic bacteria, enterococcus Piperacillin-tazobactam, 4.5 g intravenously every 6–8 hours, or ertapenem, 1 g every 24 hours
Meningitis, bacterial, age > 50 years, community-acquired Pneumococcus, meningococcus, Listeria monocytogenes,2 gram-negative bacilli, group B streptococcus Ampicillin, 2 g intravenously every 4 hours, plus ceftriaxone, 2 g intravenously every 12 hours, plus vancomycin, 15–20 mg/kg intravenously every 8–12 hours1
Meningitis, bacterial, community-acquired Streptococcus pneumoniae (pneumococcus),3 Neisseria meningitidis (meningococcus) Ceftriaxone, 2 g intravenously every 12 hours,3 plus vancomycin, 15–20 mg/kg intravenously every 8–12 hours1
Meningitis, postoperative (or posttraumatic) S aureus, gram-negative bacilli, coagulase-negative staphylococci, ...

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