One of the most common causes of bloodstream infections worlwide and causes extensive morbidity and mortality with death rates ranging from 20 to 40%.
Annual incidence is 9.3-65 casesfor 100,000 person-years in the US.
Associated with a high morbidity rate in 30 day mortality rate of 20-40%.
Approximately 30% of patients who develop S aureus will die within a year of index culture.
Causes 300,000 deaths per year worldwide.
Staphylococcus aureus is a gram-positive bacterium, existing is a commensal in the human nares, skin, throat, and G.I. tract in about 30% of people.
Gram staining shows gram-positive cocci in clusters and biochemical testing identifies the organism in a blood culture, and antibiotic susceptibility testing is then performed on the isolate.
For adults with Staphylococcus aureus bloodstream infections, the most common manifestations include hypokalemia, vomiting, diarrhea, increased liver tests, increased blood creatinine, high blood pressure, leukopenia, fever, abdominal pain, fungal infection, headache and dyspnea.
SA bacteremia causes metastatic infection in more than 1/3 of patients, including: endocarditis, 12%, septic arthritis, 7%, vertebral osteomyelitis, 4%, spinal epidural abscess, psoas abscess, septic pulmonary embolism, and seeding of implantable medical devices.
Approximately 12% of patients with S aureus bacteremia develop endocarditis.
If SA breaches the skin or mucosal barriers and access is normally sterile sites such as the bloodstream it can attach to the surface of host tissues, such as native cardiac valves, or implanted devices.
The attachment of microbial surface components, recognizing adhesive matrix molecules enable SA, to bind to many human proteins, including fibronectin, fibrinogen, collagen, von Willebrand, factor, and platelets.
After attaching to a surface SA cells produce a biofilm matrix of polysaccharides, proteins and extra cellular DNA protecting it from the protection by the human immune system.
SA then enters a low metabolic state with decreased susceptibility to antibiotics.
SA may lead to abscess formation, facilitated by clotting factors, coagulase, and von Willebrand factor binding protein, which promote fibrin clots and pseudocapsule protecting a bacterial aggregate from phagocytic clearance.
Risk factors include intravascular devices, such as implantable cardiac devices and dialysis vascular catheters, central venous catheters, recent surgical procedures, injection drug use, diabetes, hemodialysis, previous Staph aureus infection, male sex, the very young, old age, low socioeconomic status, corticosteroid use, HIV infection, and S aureus nasal colonization.
SA bacteremia that is prolonged at 48 hours or greater is associated with a 90 day mortality risk of 39%.
All patients with SA bacteria detected with blood cultures should undergo transthoracic echocardiography, as well as patients at high risk for endocarditis, such as those with persistent bacteria, persistent fever, metastatic infection foci, or implantable cardiac devices.
Despite appropriate anabiotic therapy, approximately 1/3 of patients with S aureus have persistent bacteria:mortality is higher in patients with persistent bacteria, and new metastatic foci in the infection are also more likely with delayed clearance.
Repeat blood cultures are performed for patients with S aureus in the intervals of 24 to 48 hours until blood culture results are negative.
Women have an 18% increased odds of mortality from Staph aureus bacteremia.
Glucocorticoid use is associated with a substantial increase risk of community acquired staphylococcal aureus bacteremia.
Individuals using systemic glucocorticoids have a 2.5 fold increase in the risk of community acquired staphylococcal aureus bacteremia.
The association of glucocorticoids follows a dose relationship.
Methicillin resistance is an independent risk factor for mortality.
The presence of the mecA gene confers methicillin resistance in S aureus.
Obtaining follow up blood cultures to document resolution of bacteremia after the initiation of treatment health is an appropriate management tool.
Draining abscesses and removing infected prostheses is consistent with appropriate management.
SA infective endocarditis is common and often clinically indistinguishable from Staph bacteremia and may be fatal if inadequately treated.
Patients with SA infective endocarditis should be considered no patients with Staph aureus bacteremia.
All patients should be evaluated with echocardiography, preferably by transesophageal echo cardiography, except in low risk infective endocarditis patients.
Staph aureus bacteremia is categorized as methicillin, susceptible or methicillin-resistant based on sustainability to beta lactamantibiotics.
Initial treatment typically includes antibiotics against MRSA such as vancomycin or daptomycin.
Once antibiotic susceptibility results are available, antibiotics should be adjusted.
Vancomycin and daptomycin are first line antibiotic therapies for methicillin-resistant Staph aureus bacteremia.
Cefazolin or anti-Staphylococcus penicillins can be used for methicillin susceptible SA.
Clinical trials assessing the addition of the second antibiotic to standard care has not demonstrated an improvement in clinical outcomes, and the use of combination therapies associated with adverse effects such as increased kidney injury.
With patients with uncomplicated MRSA bacteremia, at least 14 days of antibiotic therapy from the first negative culture should be adequate management.
For all other patients a course of 4-6 weeks is recommended.
In patients with low risk S aureus can receive oral antibiotics after 5 to 7 days of intravenous antibiotics as a consideration.
Among patient with complicated S aureus who achieve blood culture clearance, dalbavancin was not superior to standard therapy for achieving a more desirable outcome at day 70.
Control of the source of Staph bacteria is a critical component of care.
Procedures may include incision and drainage of abscesses, debridement of infected tissue, removal of implanted prosthetic material, and removal of indwelling intravascular catheters, and cardiac devices.
Early source control is associated with early clearance of bacteria, lower mortality.