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
- Superficial disease – culture of wound or affected area
- 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
- Prolonged exposure to staphylococci during deep-seated infection can result in elevated antibodies to staphylococcal ribitol teichoic acid (RTA)
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
- Mycobacterium tuberculosis
- Gastroenteritis
- Bacterial
- Viral
- Parasitic
- Meningitis/encephalitis
- Other bacterial
- Viral
- Fungal
- Osteomyelitis
- Malignancy
- Ewing sarcoma
- Sarcomas
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
- Immune deficiency
- Diabetes mellitus
- Hospitalization
- Indwelling catheters
- Intravenous 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
- Abscess
- 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
ARUP Laboratory Tests
Identify Staphylococcus aureus colonization
Culture/Identification
Detect presence of bacteria in blood
Testing is limited to the University of Utah Health Sciences Center only
Continuous Monitoring Blood Culture/Identification
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
Stain/Culture/Identification
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
Automated Broth Microdilution
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
Qualitative Polymerase Chain Reaction
Aid in diagnosis of staphylococcal disease
Negative result does not exclude staphylococcal disease
Positive antibody assay does not denote protection from subsequent infection
Semi-Quantitative Immunodiffusion
Medical Experts
Delgado

Fisher

References
19374581
18162929
Gorwitz RJ. A review of community-associated methicillin-resistant Staphylococcus aureus skin and soft tissue infections. Pediatr Infect Dis J. 2008;27(1):1–7.