Staphylococcus aureus

Background

• Staphylococcus aureus is a ubiquitous human pathogen associated with a broad spectrum of clinical illnesses including skin and soft tissue infections, pulmonary infections, bone and joint infections, bacteremia, and infective endocarditis as well as toxin-mediated diseases.
• Staphylococcus aureus produces many virulence factors that contribute to pathogenicity and development of methicillin resistance.
• Staphylococcus aureus may form a biofilm on a variety of host and host-associated surfaces which may increase resistance to host clearance factors and antimicrobials.
• Populations at increased risk of infection include:
  • individuals colonized with Staphylococcus aureus.
  • infants and elderly persons.
  • those having invasive medical interventions or other healthcare contact.
  • IV drug users.
  • communal/crowded living or sharing of personal items.
  • men who have sex with men.
  • immunocompromised individuals, including those with HIV/AIDS.
  • presence of foreign materials in the body, such as sutures, IV catheters, prosthetic joints or valves.
  • those with medical comorbidities such as; peritoneal dialysis, hemodialysis, diabetes mellitus, rheumatoid arthritis, poor functional status, and antibiotic use.
• Transmission occurs primarily via direct contact with colonized persons or fomites.

Evaluation

• Diagnosis is typically based on isolation of the organism from the involved site or identification through molecular testing.
• Identifying S. aureus through preoperative screening or screening for carriers can be performed using cultures or polymerase chain reaction.
• Systemic infections are usually identified by culturing sterile sites with blood culture or aspiration.

Management

• Management varies by clinical manifestation but general principles include source control, such as abscess drainage or removal of any indwelling device when feasible, and prompt administration of appropriate antibiotics.
• Selection of antibiotic and route of administration vary by clinical manifestation.
  • For methicillin-susceptible Staphylococcus aureus
    • an antistaphylococcal penicillin (such as nafcillin) or cefazolin are generally preferred for serious infections.
    • dicloxacillin or cephalexin is often preferred when S. aureus is the known cause for mild infections; clindamycin is an alternative.
  • For methicillin-resistant strains of S. aureus (MRSA)
    • vancomycin is generally preferred for serious infections with several alternative options including; linezolid, daptomycin, ceftaroline, telavancin, dalbavancin, and tigecycline.
    • co-trimoxazole (trimethoprim/sulfamethoxazole) and doxycycline are options for mild community-acquired infections.
  • Duration of therapy and need for a second antimicrobial agent in serious infections is dependent on the site involved and presence of a foreign body, such as a prosthetic heart valve.
• Surgical intervention may be required for patients with S. aureus infections causing infective endocarditis, skin and soft tissue infections, and osteoarticular infections.