Staphylococcal Disease

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). Laboratory studies used in the diagnosis generally include culture and serum antibody testing.

Diagnosis

Indications for Testing

  • Pustular disease
  • Abscess, cellulitis

Laboratory Testing

  • Culture
    • Superficial disease – culture of wound or affected area
      • Recommend incision and drainage of all abscesses for wound culture
      • Further testing by polymerase chain reaction (PCR) for the mecA/mecC genes 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

Background

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
  • 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

ARUP Laboratory Tests

Identify Staphylococcus aureus colonization

Detect presence of bacteria in blood

Important informationTesting is limited to the University of Utah Health Sciences Center only

Identify bacteria in wounds

Anaerobe culture is recommended for body fluids, tissue, and deep wound/surgical cultures; refer to anaerobe culture and gram stain

Anaerobe culture is NOT included with this order

Determine in vitro susceptibility to antimicrobial agents for Staphylococcus spp

The following agents are tested – clindamycin, daptomycin, erythromycin, gentamicin, levofloxacin, linezolid, nitrofurantoin, oxacillin, penicillin, quinupristin/dalfopristin, rifampin, tetracycline, trimethoprim/sulfamethoxazole, and vancomycin

For serious infections with coagulase-negative staphylococci, testing for the presence of the mecA gene may be appropriate and will be performed in order to interpret the results for beta-lactam agents

For mecA gene testing, refer to the antimicrobial susceptibility test for mecA gene by polymerase chain reaction (PCR)

Selective reporting by organism and source

Gold standard for detecting oxacillin/nafcillin resistance in Staphylococcus species

Determine presence of the mecA/mecC genes that confer resistance to nearly all beta-lactam antibiotics

Refer to antimicrobial susceptibility (Staphylococcus) test for susceptibility panel testing for Staphylococcus spp

For detection of colonization, order Staphylococcus surveillance culture

Aid in diagnosis of staphylococcal disease

Negative result does not exclude staphylococcal disease

Positive antibody assay does not denote protection from subsequent infection

Medical Experts

Contributor

Delgado

Julio Delgado, MD, MS
Executive Vice President, ARUP Laboratories
Division Chief of Clinical Pathology, University of Utah and ARUP Laboratories
Professor of Clinical Pathology, University of Utah
Medical Director, Protein Immunology and Immunologic Flow Laboratories, ARUP Laboratories
Contributor

Fisher

Mark A. Fisher, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Bacteriology, Special Microbiology, and Antimicrobial Susceptibility Testing, ARUP Laboratories

References

Additional Resources
Resources from the ARUP Institute for Clinical and Experimental Pathology®