Staphylococcus aureus bacteria are gram-positive cocci that causes superficial skin infections such as folliculitis, impetigo, and cellulitis and as well as deep-seated infections such as endocarditis, osteomyelitis and tissue abscesses.

Epidemiology

• Incidence
  • Cellulitis accounts for 2% of outpatient office visits
  • Deep-seated infections are uncommon
• Transmission
  • Portal of entry for superficial infections may be a surface abrasion but is frequently unknown
  • For deep infections, portal of entry may be a surgical site or indwelling catheter

Organism

• Gram positive cocci; coagulase positive
• May acquire drug resistance and be called methicillin resistant staphylococcus aureus (MRSA)

Risk Factors

• Immune deficiency
• Diabetes mellitus
• Hospitalization
  • Indwelling catheters
• Intravenous drug use (IVDU)
• Primary viral exanthem (e.g., varicella zoster)
• Alcohol abuse
• Local trauma, lymphedema

Clinical Presentation

• Superficial skin infections
  • Folliculitis
  • Impetigo
  • Cellulitis
    • More commonly caused by beta-hemolytic streptococcus; infection penetrates the subcutaneous tissue layer
    • Erythema and warmth, swelling and tenderness of affected area
  • Staphylococcal scalded skin syndrome
• Soft tissue infections
  • Abscess
    • >50% are caused by staphylococcus
    • Includes furuncles and carbuncles
    • Area of fluctuance and erythema demarcate the abscess
  • Necrotizing fasciitis
    • Type 1 is frequently caused by staphylococcus
    • Rapid progression of local symptoms, including systemic symptoms (eg, fever)
      • Pain out of proportion to involvement
      • Marked edema
      • Crepitants when palpated
    • Toxic shock syndrome
• Deep infections
  • Endocarditis - usually associated with prosthetic valves, indwelling catheters, or intravenous drug use
  • Osteomyelitis - frequently associated with underlying immune deficiency
  • Deep tissue and muscle abscesses
• Other infections
  • Pneumonia
  • Septic thrombophlebitis
  • Gastroenteritis - food poisoning, rapid onset vomiting and diarrhea

Treatment

• Superficial - frequently cured with antibiotic therapy and abscess drainage
• Deep - involves tissue debridement and abscess drainage

Diagnosis

• Indications for testing
  • Pustular disease; abscess, cellulitis
  • Bacteremia associated with deep-seated staphylococcal infection may present a puzzling picture since the focus of infection may not be readily apparent
• Laboratory testing
  • Culture
    • Superficial disease - culture of wound or affected area; recommend incision and drainage of all abscesses for wound culture
    • Deep-seated infections - culture of the organism from appropriate clinical specimens
  • Prolonged exposure to staphylococci during deep-seated infection can result in elevated antibodies to staphylococcal ribitol teichoic acid
    • High antibody levels (1:2 or greater) against staphylococcal ribitol teichoic acid in patients with staphylococcal bacteremia indicates staphylococcal endocarditis or complicated staphylococcal bacteremia

Differential Diagnosis

• Streptococcal infection
• Clostridial infection
• Gram-negative infection