• Usually caused by endogenous organisms
• Occurs when there is a break in a mucocutaneous barrier
• Infections are often polymicrobial and include aerobic organisms
• Increased risk associated with impaired host immunity or presence of devitalized tissue (due to surgery, trauma, vascular insufficiency)
• Numerous virulence factors including exotoxins (e.g., Clostridia spp.), antiphagocytic capsule (e.g., Bacteroides spp.), endotoxin (gram-negative anaerobes)
• Infections may be characterized by suppuration, abscess formation, or tissue destruction

• Less frequent in children than in adults
• Responsible for up to 10% of significant bacteremic episodes in infants and children

• Vary with nature of infection

• Determined by speed with which infection is appropriately treated with surgery and antibiotics
• Up to 40% mortality associated with clinically apparent anaerobic bacteremia
• Soft-tissue infections caused by Clostridial spp. may cause up to 20% mortality despite aggressive therapy

• Central nervous system (CNS) infections
  • Brain abscess
  • Subdural empyema
  • Epidural abscess
• Head and neck infections
  • Sinusitis
  • Chronic otitis media
  • Ludwig angina
  • Cervical adenitis
  • Peritonsillar abscess
  • Dental abscess
  • Gingivitis
• Pleuropulmonary infections
  • Aspiration of oral and/or gastrointestinal fluids
  • Secondary to aspirated foreign bodies
  • Actinomycosis
• Peritonitis/peritoneal abscess
  • Appendiceal abscess
  • Perforated viscus
  • Postoperative complication
  • Trauma related
• Cholangitis
  • Ascending infection may occur following Kasai procedure
  • Infection is often polymicrobial
• Bacteremia
  • Often associated with underlying GI disease
• Soft-tissue infection
  • Paronychia
  • Crepitant cellulitis
  • Necrotizing fasciitis
  • Gas gangrene
• Infected bite wounds
  • Anaerobes isolated from 50% of human or animal bites

• Likely pathogens not recovered from aerobic cultures
• Failure of empiric antibiotic coverage that is not active against anaerobes

Question: Impaired mental status?
Significance: Increased risk of aspiration.

Question: History of thumbsucking?
Significance: Anaerobes frequently isolated from paronychia.

Question: Recent surgery or trauma?
Significance: Poor drainage leads to infection.

Question: Underlying immunodeficiency or chronic illness?
Significance: Impaired phagocytic function.

Question: Discharge with foul odor?
Significance: Characteristic of anerobic infection.

Finding: Location of infection
Significance: Increased incidence of anaerobic infections associated with oropharyngeal, abdominal, and female genital tract

Finding: Poor dentition
Significance: Increased colonization of oropharyax with anaerobic organisms

Finding: Gas in tissue, crepitus
Significance: Infection with gas-forming organism

Finding: “Dishwater” pus
Significance: Characteristic of anaerobic infections

Test: Gram stain
Significance: Small, pleomorphic gram-negative bacilli (Bacteroides spp.); large gram-positive organisms with “box-car” morphology (Clostridia spp.)

Test: Anaerobic cultures
Significance: Should be performed on tissue or aspirated fluid obtained in a sterile fashion from the infected site. Avoid sending a swab for culture. Specimens need to be transported promptly to the microbiology laboratory.

Test: Antibacterial susceptibility testing
Significance: Due to usual efficacy of empiric regimens, susceptibility studies should be limited to organisms involved in potentially life-threatening or difficult-to-treat infections.

Test: X-ray studies
Significance: Air-fluid level, cavity formation, gas in tissue

Test: Special imaging studies
Significance: CT and/or MRI scans often important to define anatomical location and extent of disease.

• CNS infections
  • Cefotaxime/metronidazole or oxacillin/chloramphenicol
• Head and neck infections
  • Penicillin or clindamycin
• Pleuropulmonary infections
  • Penicillin or clindamycin or ampicillin/sulbactam
• Peritonitis/peritoneal abscess
  • Ampicillin/sulbactam or cefoxitin
• Cholangitis
  • Ampicillin/sulbactam and gentamicin
• Bacteremia
  • Isolate-dependent
• Soft-tissue infection
  • Site-dependent
• Infected bite wounds
  • Amoxicillin/clavulinic acid

• Surgery
  • Effective drainage of abscesses and debridement of devitalized tissue essential
• Hyperbaric oxygen
  • Especially for extensive Clostridial infections

Dunkle LM. Anaerobic infections. In: Feigin RD, Cherry JD, eds. Textbook of pediatric infectious diseases, 3rd ed. Philadelphia: WB Saunders, 1992:1044–1052.

Finegold SM. Anaerobic bacteria: general concepts. In: Mandell GL, Douglas RG, Bennett JE, eds. Principles and practice of infectious diseases, 4th ed. New York: Churchill Livingstone, 1995:2156–2173.

Goldstein EJ. Selective nonsurgical anaerobic infections: therapeutic choices and the effective armamentarium. Clin Infect Dis 1994;18:S273–S279.

Gorbach SL. Antibiotic treatment of anaerobic infections. Clin Infect Dis 1994;18:S305–S310.

Nichols RL, Smith JW. Anaerobes from a surgical perspective. Clin Infect Dis 1994;18:S280–S286.