Staphylococcal Infections Workup

Updated: Mar 09, 2022
  • Author: Thomas E Herchline, MD; Chief Editor: John L Brusch, MD, FACP  more...
  • Print

Laboratory Studies

Obtain cultures (with susceptibilities) as appropriate for the site of infection. Blood cultures may be positive for staphylococcal species, even when results from other cultures are negative. Obtain blood cultures from all patients with serious infections.

Deck et al have demonstrated a high sensitivity for S aureus (99.5%) and CoNS from positive blood cultures using a PNA FISH method. Turnaround times were less than 30 minutes. [29]

Patients with S aureus bacteremia should undergo repeat cultures after starting appropriate therapy. Patients with persistent bacteremia (after ≥3 days of appropriate therapy) are more likely to have underlying endocarditis.

CBC count usually reveals leukocytosis with a left shift (bands). Patients with chronic staphylococcal infection may have thrombocytosis.

Erythrocyte sedimentation rate and C-reactive protein may be helpful in patients with subacute or chronic infections such as osteomyelitis.

Teichoic acid antibody titers in patients with continuous S aureus bacteremias suggest a deep-seated (not intravenous line) focus (eg, endocarditis, abscess, osteomyelitis).

Screening tests for nasal colonization with methicillin-resistant S aureus (MRSA) are not predictive of the subsequent development of MRSA pneumonia (sensitivity, 23%) or MRSA bloodstream infection (sensitivity, 24%). [30]


Other Tests

Patients with S aureus or S lugdunensis bacteremia should undergo echocardiography. [31] Some experts recommend transesophageal echocardiography (TEE) in all patients without contraindications to rule out S aureus endocarditis. [32] Several scoring systems have been developed to be more selective in this determination. [33] High-risk factors for endocarditis include persistence of positive blood cultures for 5 days or longer while on appropriate antibiotic therapy, presence of a long-term indwelling intravenous catheter or device, and presence of a prosthetic heart valve.