Assessing and monitoring patients with Staphylococcus aureus bacteraemia

Take blood samples for repeat culture 48 to 72 hours after starting antibiotics for Staphylococcus aureus bacteraemia, and repeat every 2 days until the first negative culture result. In children, sampling may be performed more frequently because bacteraemia can clear quickly, and the duration of therapy is often measured from the time of the first negative blood culture result.

It is essential to closely monitor patients to detect relapse of bacteraemia or the development of metastatic infection, including infective endocarditis. Haematogenous seeding of prosthetic material (eg prosthetic joints) by S. aureus can result in metastatic infection at the prosthetic site (eg arthroplasty device infections, prosthetic valve endocarditis). In adults and children with bacteraemia lasting 7 days or longer, re-evaluate for endocarditis and other metastatic foci.

In adults, echocardiography must be performed to excluded infective endocarditis. Echocardiography is most sensitive at days 5 to 7; however, request earlier echocardiography if the patient has signs of endocarditis (eg heart murmur). The choice of transthoracic echocardiogram (TTE) or transoesophageal echocardiogram (TOE) is controversial. Although TOE is more invasive, it is significantly more sensitive than TTE and is therefore preferable for adults:

• with abnormal heart valves on TTE or a history of valvular heart disease
• with a cardiac implantable electronic device (CIED) or a prosthetic heart valve
• if there is poor visualisation of the heart valves with TTE
• if there is a high suspicion of endocarditis.

If a TTE is negative in an adult with suspected prosthetic valve and CIED-associated endocarditis, arrange a TOE if possible.

If the diagnosis remains uncertain after echocardiography, especially in adults with complex anatomy or suspected paravalvular complications, consider multimodal imaging using techniques such as cardiac computed tomography (CT) and cardiac magnetic resonance imaging (MRI) with or without 18F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG-PET). If endocarditis is confirmed, see Staphylococcal endocarditis for treatment regimens and duration of therapy.

In children, do not perform echocardiography unless the child has an intracardiac or valvular abnormality, prolonged fever, suspected endocarditis, or positive blood culture results beyond 72 hours. TTE is usually preferred to TOE in children.