Patients presenting to the hospital with MRSA pneumonia: differentiating characteristics and outcomes with empiric treatment

Background: Concern for MRSA in patients presented to the hospital with pneumonia may be overestimated leading to excessive prescribing of empiric anti-MRSA therapy. This study aims to identify at-risk patients and treatment outcomes. Methods: Adults hospitalized during 2005-2011 with pneumonia diagnosed within 48 h of admission were included. Medical charts were retrospectively reviewed for relevant data. Patients with MRSA were matched 1: 1 to those with non-MRSA pathogen or negative culture. A published risk scoring system for MRSA pneumonia was applied. Results: 268 elderly patients were included, 134 patients in each group. Compared to non-MRSA group, MRSA patients presented more acutely ill (p < 0.0001) (pneumonia severity index score, 150 vs 93; vasopressor therapy, 34% vs 6%; ICU admission, 47% vs 13%; and mechanical ventilation, 35% vs 10%) and had worse outcomes (p < 0.0001) (time to reach clinical stability, 6 vs 2.5d; length of stay, 10 vs 5d; clinical failure, 28% vs 4%; 28-day mortality, 22% vs 3%). When applied to our patients, a published risk scoring scheme had 93% sensitivity but lacked specificity at 55%; 40% of medium-risk patients did not have MRSA. A history of MRSA infection or pneumonia differentiated the latter group. Most MRSA patients (66%, 88/134) were treated empirically (primarily vancomycin) but outcome was not improved by receipt of empiric therapy. Conclusions: Use of a published risk scoring scheme with additional variables from this study can potentially reduce overprescribing of anti-MRSA empiric therapy in patients presented to the hospital with pneumonia. Prospective studies evaluating the treatment benefit of non-vancomycin alternatives as empiric therapy are needed.