Assessment of potential routes of infection, routes of transmission, and secondary sites of infection

Overview

Identifying the primary route of entry and any secondary (metastatic/disseminated) sites of infection is central to both diagnosis and management planning - a bacteraemia's primary source (line, urinary, intra-abdominal, skin) and any seeded secondary sites (endocarditis, discitis, septic arthritis, abscess) both require identification for complete treatment
A systematic consideration relevant to essentially any bacteraemic or systemically unwell patient, since incomplete source identification risks undertreating an unrecognised secondary focus

Haematogenous spread from a primary source can seed distant secondary sites, particularly favouring certain tissues (heart valves, bone, joints) depending on organism and patient risk factors - Staphylococcus aureus bacteraemia in particular has a high propensity for metastatic seeding, making thorough secondary-site assessment especially important with this organism

Systematic assessment: history (recent procedures, skin breaks, intravenous drug use, dental work), examination (skin, joints, spine, cardiac auscultation for new murmur), and targeted imaging/echocardiography guided by symptoms and organism-specific risk (e.g. echocardiography is now often recommended for all Staphylococcus aureus bacteraemia given the high metastatic seeding risk, not only when clinically suspected)

Identified secondary sites (endocarditis, discitis, septic arthritis) require treatment duration extension and, sometimes, source control (drainage, valve surgery) beyond what would be needed for the primary bacteraemia alone
Missing a secondary site risks undertreating that focus even if the primary source and bloodstream infection appear to respond to initial treatment

Staphylococcus aureus bacteraemia (high metastatic seeding risk, echocardiography consideration), discitis-osteomyelitis as an occult secondary site, septic arthritis as a metastatic seeding site, persistent bacteraemia as a marker of an unaddressed secondary focus
Staphylococcus aureus bacteraemia carries a sufficiently high risk of metastatic seeding (endocarditis, discitis, septic arthritis) that echocardiography and careful secondary-site assessment are recommended even without specific localising symptoms, reflecting this organism's particular propensity for haematogenous spread compared with many other bacteraemia-causing organisms

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