ID Board Review/Bacterial Diseases/Gram-positive cocci (GPC)/Staphylococcus aureus

Clinical Presentations

 * Skin Infections (most common presentations of S. aureus)
 * Cellulitis
 * Impetigo
 * Folliculitis
 * Mastitis
 * Infection Surgical Wounds
 * Infective Endocarditis, especially patients with left-sided valvular heart disease and patients with IV drug use
 * S. aureus is often a cause of Osteomyelitis, and is the most common cause of Septic Arthritis
 * S. aureus is the most common cause of Spinal Epidural Abscesses and Suppurative Intracranial Phlebitis
 * Rarely causes meningitis, but when it does, it's usually after trauma, or Neurosurgery
 * S. aureus rarely causes community pneumonia, but is often the cause of Nosocomial (Hospital Acquired) Pneumonia
 * Septic Shock
 * Prosthetic Joint Infection

Risk Factors

 * Skin/mucosal breaks or tears
 * Foreign body/implant presence
 * Prior viral illness (especially superimposed bacterial pneumonia)
 * Defects in cellular or humoral immunity

Diagnosis

 * Bacteremia: Blood culture; low threshold for getting infective endocarditis blood cultures
 * Sensitivities to differentiate between MSSA and MRSA
 * MRSA Nares Swab PCR (to r/o MRSA pneumonias)

Differential Diagnoses

 * For skin infections without pus, consider Streptococcus

Resistance Mechanism(s)

 * Mec A gene → MRSA