Staphylococcus Aureus Pneumonia: Emergence of MRSA in the Community

Suzanne F. Bradley, MD

Disclosures

Semin Respir Crit Care Med. 2005;26(6):643-649. 

In This Article

Detection of CA-MRSA

Most medical centers cannot perform typing for SCCmecIV or other molecular methods to detect CA-MRSA. Currently, the diagnosis is suspected based on a clinical presentation consistent with severe staphylococcal infection and lack of patient risk factors for HA-MRSA. Patients with CA-MRSA are significantly younger (median age 23 years vs 68 years) and without significant health problems (85% vs 24%) than patients with HA-MRSA.[18] The diagnosis of CA-MRSA should also be considered in severely ill young persons with a preceding history of influenzalike illness, severe respiratory symptoms, high fever, hemoptysis, leukopenia, and hypotension.[2]

As CA-MRSA becomes more widespread in health care facilities, epidemiological definitions based on place of acquisition and risk factors for MRSA will be less useful. For this reason, experts recommend that appropriate cultures from samples of blood, sputum, skin and soft tissue, and other sources be obtained as early as possible rather than relying on clinical criteria alone and empirical treatment. Cultures of sputum are 92% sensitive for the detection of S. aureus.[14] However, the presence of a positive sputum culture for S. aureus is not specific for infection and may represent oropharyngeal colonization in patients with suspected pneumonia.

Currently, CA-MRSA is likely if the isolate is resistant to all β-lactam antibiotics and susceptible to most other antibiotic classes such as aminoglycosides. lincosamides, sulfonamides, fluoroquinolones, and macrolides. CA-MRSA isolates are significantly more likely to be susceptible to gentamicin (94% vs 80%), clindamycin (83% vs 21%), ciprofloxacin (79% vs 16%), and erythromycin (44% vs 9%) than HA-MRSA isolates.[18] Unfortunately, as CA-MRSA becomes more common, it is likely that it too will acquire resistance genes that will make detection by routine antimicrobial susceptibility testing more difficult.

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