Staphylococcal Disease

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
    • Further testing by PCR for mecA to rule out resistant staphylococci
  • Deep-seated infections – gram stain and culture of the organism from appropriate clinical specimens
• Serum antibody testing
  • Prolonged exposure to staphylococci during deep-seated infection can result in elevated antibodies to staphylococcal ribitol teichoic acid (RTA)
    • High antibody levels (≥1:4) against staphylococcal RTA in patients with staphylococcal bacteremia may indicate staphylococcal endocarditis or complicated staphylococcal bacteremia

Differential Diagnosis

• Soft-tissue and skin infections
  • Streptococcal infection
  • Gram-negative infection
• Deep infections
  • Clostridial infection
• Pneumonia
  • Viral – hantavirus, influenza virus, other respiratory viruses
  • Other bacterial – Haemophilus influenzae, Chlamydophila pneumoniae, Mycoplasma pneumoniae
  • Fungal – Pneumocystis jirovecii
  • M. tuberculosis
• Gastroenteritis
  • Bacterial
  • Viral
  • Parasitic
• Meningitis/encephalitis
  • Other bacterial
  • Viral
  • Fungal
• Osteomyelitis
• Malignancy – Ewing sarcoma, sarcomas

Clinical Background

Staphylococcus aureus bacteria are gram-positive cocci that cause diseases of varying severity, from skin and soft-tissue infections (eg, folliculitis, impetigo, cellulitis, abscesses) to deep-seated infections (eg, endocarditis, osteomyelitis).

Epidemiology

• Incidence – 28-35/100,000
• Transmission
  • Portal of entry for superficial infections is frequently unknown but may be from a surface abrasion 
  • Portal of entry for deep infections includes surgical sites or indwelling catheters

Organism

• Gram-positive cocci; coagulase positive
• May acquire drug resistance, including resistance to nearly all beta-lactam agents 
  • Known as methicillin-resistant Staphylococcus aureus (MRSA)

Risk Factors

• Methicillin-sensitive Staphylococcus
  • Immune deficiency
  • Diabetes mellitus
  • Hospitalization
  • Indwelling catheters
  • IV drug use (IVDU)
  • Primary viral exanthem (eg, varicella-zoster)
  • Alcohol abuse
  • Local trauma, lymphedema
  • Colonization
• MRSA
  • Antibiotics in past month (odds ratio 2.4)
  • Abscess (odds ratio 1.8)
  • Reported spider bite (odds ratio 2.8)
  • History of MRSA (odds ratio 3.3)
  • Close contact with MRSA patient (odds ratio 3.4)
  • Snorting or smoking illegal drugs (odds ratio 2.9)
  • Incarceration ≤12 months (odds ratio 2.8)

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 frequently caused by Staphylococcus
    • Rapid progression of local symptoms, including systemic symptoms (eg, fever)
      • Pain out of proportion to apparent involvement
      • Marked edema
• Deep infections
  • Endocarditis – associated with native and prosthetic valves, indwelling catheters, or IVDU
  • Osteomyelitis – frequently associated with underlying immune deficiency
  • Deep tissue and muscle abscesses
  • Septic arthritis – associated with implanted joints, rheumatoid arthritis, immunocompromised state
• Other infections
  • Pneumonia/empyema
  • Septic thrombophlebitis/pulmonary emboli
  • Gastroenteritis – food poisoning, rapid onset vomiting, and diarrhea
  • Meningitis/brain abscesses/vertebral abscesses
  • Toxic shock syndrome

Treatment

• Superficial – frequently cured with topical or systemic antibiotic therapy and abscess drainage
• Deep – involves tissue debridement/abscess drainage and systemic antibiotic therapy

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory