Staphylococcus aureus bacteremia (SAB) is a common and serious infection with mortality rates of up to 40%. Most of the time clinical microbiologists in the UK usually provide telephone advice to the primary clinical care team when blood cultures become positive. Bedside clinical review only occurs in center with infectious disease services. Infectious disease consultation in these patients leads to improvements in clinical management and, is associated with lower rate of recurrent disease and reduction in mortality.
According to the Infectious Diseases Society of America (IDSA) guidelines –
- Additional blood cultures 2-4 days after initial positive cultures and as needed thereafter are recommended to document clearance of bacteremia (A-II).
- Echocardiography is recommended for all adult patients with bacteremia. Transesophageal echocardiography (T0E) is preferred over transthoracic echocardiography (TTE) (A-II).
Background
Staphylococcus aureus is a catalase positive, coagulase positive gram-positive coccus. It is also a kind skin colonizer and is found in the anterior nares of 10-40 % of people. Staphylococcus aureus possesses many virulence factors of which the clinically important ones are the ability to form a biofilm (especially in patients with prosthetic materials in-situ), producing toxins like Toxic Shock Syndrome Toxin (TTST-1) and Panton-Valentine leucocidin (PVL).
It can cause a wide range of clinical infections viz skin and soft tissues infections, bone and joint infections, endocarditis, prosthetic device-related infections, respiratory tract infection and urinary tract infections.
There are Methicillin-sensitive S.aureus (MSSA) and Methicillin-resistant S. sureus (MRSA). For Methicillin -sensitive S.aureus (MSSA) infections, beta-lactam agents are effective and preferred agents. Beta-lactam agents include penicillin and its derivatives (Flucloxacillin, Amoxicillin..etc) , cephalosporin (Cefalexin, cefotaxime, Cefuroxime , Ceftriaxone, Ceftazidime ..etc) , beta-lactam and beta lactamase inhibitor combination (Co-amoxiclav , Piperacillin-tazobactam) and carbapenem (meropenem, ertapenem, Imipenem).
Methicillin-resistance S. aureus (MRSA) is determined by the presence of penicillin-binding protein, PBP 2a, which confers resistance to all β-lactam agents. Generally speaking, different groups of antibiotics viz glycopeptides, Linezolid, Daptomycin, 5th generation cephalosporin Ceftaroline and potential alternatives including Doxycycline and Clindamycin can be used in treating MRSA infections. Choice of antibiotics should be guided by sensitivity, extent of infection, allergy status and patient tolerance.
When it comes to management of these patients, history taking and physical examination are important to determine the most likely source of infections and formulate further management plan. In addition to these, it is important from the microbiology point of view to know about previous staphylococcal infections, risk of MRSA including previous colonization, allergy status and nature of allergy.
Management varies greatly and depends on source of infections. Staphylococcus aureus bacteremia (SAB) alone will need a minimum of 14 days of treatment from first negative blood culture and longer if recurrence occurs with no obvious source of infection identified. Obviously, prolonged duration of antibiotics will be needed if there is deep seated source like endocarditis, septic arthritis, osteomyelitis or discitis. Source control is very important in managing patients with deep seated infection. It is also crucial to involve specialties (endocarditis team, spinal team or orthopedic team) as indicated and MDT (multi-disciplinary team) discussion would benefit in overall patient’s management.
As a ground rule, Staphlococcus aureus bacteriaemia (SAB) patients need repeat blood culture every 48 hours until blood culture is negative and at least to start with transthoracic echo TTE (although Transesophageal echo TOE is gold standard investigation) to make sure there are no features suggestive of endocarditis. Being low threshold to proceed relevant imaging (i.e MRI Spine or MRI of affected joint) as there is high risk of seeding of infection as well as it could potentially be the source of infection. Last but not least, consider involving Infection specialist earlier in centers where infectious disease services are available which is proven reduction in mortality.
References
- Liu, C et al (2011) Clinical Practice Guidelines by the Infectious Disease Society of America for the treatment of Methicillin-Resistant Staphylococcus aureus infections in Adults and Children . Vol 52, Issue3, Pages e18-e55, Clinical Infectious Diseases. https://doi.org/10.1093/cid/cir353
- Török, Estée, Cooke, Fiona J., Moran, Ed (2017) Oxford handbook of infectious diseases and microbiology. 2nd edition Oxford Pages 34,234-236; New York: Oxford University Press
Author Information
Phyu Min Thet
ST 4 Infectious Disease/ Medical Microbiology trainee
Leeds Teaching Hospital NHS Foundation Trust
Yorkshire and Humber, West Yorkshire
