Start treatment without delay in patients at risk
Standard empiric treatment options for hospitalized patients with CAP (with the exception of those in the ICU) include either a beta-lactam and azithromycin or a respiratory fluoroquinolone (neither of which is active against MRSA).1 All patients who are hospitalized for CAP should be started on this regimen without delay. If gram-positive cocci in clusters suggestive of S aureus are isolated from sputum, this standard empiric regimen should be adequate until further microbiologic identification is available.1 While most cases of S aureus CAP are not MRSA, the increased mortality rate associated with inappropriate antibiotic selection led the IDSA/ATS to recommend broader empiric coverage for MRSA for patients with risk factors for S aureus.1
CA-MRSA strains are distinct from their nosocomial counterpart, and the optimal therapy for confirmed CA-MRSA CAP has not been determined. Frequently, CA-MRSA isolates are sensitive to TMP-SMX, clindamycin, and fluoroquinolones. But neither fluoroquinolones nor TMP-SMX have a clear effect on toxin production, and bacterial resistance frequently emerges during therapy with clindamycin.1
The IDSA/ATS guidelines recommend either vancomycin or linezolid for CAP due to CA-MRSA, and these are the most widely used drugs for invasive CA-MRSA infections. Linezolid has been recognized as having a theoretical advantage in treating pneumonia, as it achieves higher lung epithelial concentrations than vancomycin.6 Particularly in cases of necrotizing CA-MRSA pneumonia, vancomycin has not been found to decrease toxin production, and linezolid is therefore the preferred treatment.1 Because of the limitations of vancomycin, we chose linezolid for our patient.
Treatment duration is not evidence-based
Although most patients with CAP are treated for 7 to 10 days, there are few well-designed studies evaluating the optimal time frame. Guidelines for the duration of antibiotics for CAP recommend a minimum of 5 days of therapy, presuming the patient is clinically stable.1,7 Short-duration therapy for patients with bacteremic S aureus CAP infection has been associated with an increased risk of endocarditis, and the presence of pulmonary cavities may warrant prolonged therapy.1 Our patient had an isolate of S aureus with intermediate susceptibility to moxifloxacin, which likely explains her rapid response to linezolid. She remained on linezolid for 8 days.
PRACTICE POINTERS
• Consider CA-MRSA as a cause of CAP, especially in cases in which the presentation is severe, as the guidelines for empiric treatment of CAP feature antibiotics that are not active against the CA-MRSA pathogen.
• Order sputum cultures for all patients admitted to the ICU, as well as for patients with a clinical presentation suggestive of CAP who abuse alcohol, have severe asthma or other lung disease, or have a pleural effusion.
• Start patients with CA-MRSA CAP on linezolid without delay.
The author reported no potential conflict of interest relevant to this article.