Diagnosis Problems Blamed for 30-fold Overuse of MRSA Drugs

Janis C. Kelly

June 16, 2016

Current clinical guidelines for identifying methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission are resulting in 30 times more patients with pneumonia being treated with anti-MRSA drugs than theoretically necessary because clinicians have no better options than empiric anti-MRSA therapy for many patients with community-acquired pneumonia (CAP), researchers report in an article published online May 8 in Clinical Infectious Diseases.

The multicenter, prospective surveillance study led by Wesley H. Self, MD, MPH, associate professor of emergency medicine, Vanderbilt University Medical Center, Nashville, Tennessee, showed a MRSA prevalence of 0.7% in adults hospitalized for CAP but treatment of 29.8%, nearly one third of patients with CAP, with the anti-MRSA antibiotics vancomycin or linezolid.

Accurate Clinical Prediction Model for MRSA CAP Seen as Unlikely

The authors write, "Although the identification of risk factors and development of clinical prediction models for MRSA CAP have generated great interest recently, our results suggest it is unlikely that a clinical prediction model could be developed that accurately identifies MRSA CAP at hospital admission due to the nonspecificity of common MRSA features (influenza coinfection, multilobar infiltrates) and uncommon occurrence of more specific features (massive hemoptysis, cavitary pneumonia)."

This has resulted in widespread overuse of anti-MRSA therapy because clinicians have no quick and reliable way to differentiate between non-MRSA CAP and potentially fatal MRSA.

Dr Self's team documented these problems using data from the Etiology of Pneumonia in the Community (EPIC) study of patients hospitalized for CAP. The analysis included patients enrolled between January 1, 2010, and June 30, 2012, at three hospitals in Chicago, Illinois, and two in Nashville. Eligibility criteria included age older than 18 years, hospital admission for acute respiratory infection, and radiographic evidence of pneumonia. Exclusion criteria included recent hospitalization, nursing home resident not functionally independent, and various conditions such as cystic fibrosis, cancer, tracheostomy, recent stem cell transplant, bronchiolitis obliterans, or HIV with CD4 count lower than 200 mm3.

The study population of 2259 patients underwent at least one diagnostic test for both bacteria and viruses.

The analysis showed that 1.6% of patients had CAP caused by S aureus, including 0.7% with MRSA and 1.0% with methicillin-susceptible S aureus (MSSA). The researchers examined prevalence of MRSA CAP by age group (18-49, 50-64, 65-79, and ≥80 years) and it was less than 1% in each age group.

Empirical Anti-MRSA Therapy Supported for Intensive Care Patients

The low prevalence (0.1%) of MRSA CAP among patients not admitted to an intensive care unit provides support for the current Infectious Diseases Society of America and American Thoracic Society CAP guidelines, which do not recommend routine anti-MRSA antibiotics for patients admitted to a general medical floor. Among patients admitted to an intensive care unit, MRSA CAP prevalence was 2.7%.

Patients with MRSA CAP were more likely to be admitted to an intensive care unit, had longer median hospital stays, were more likely to require mechanical ventilation, and had higher in-hospital mortality than patients with MSSA or who had CAP without S aureus. The authors advise that empirical anti-MRSA therapy for critically ill patients with CAP be considered while awaiting the results of diagnostic testing.

Rapid Test for S aureus Needed to Reduce Overuse of anti-MRSA Drugs

The authors conclude, "While MRSA CAP patients generally had high severity of illness, clinical and epidemiologic characteristics overlapped substantially with non-S. aureus CAP, particularly pneumococcal CAP, making it difficult to distinguish between etiologic types of pneumonia clinically. Low prevalence of MRSA combined with a lack of highly distinctive clinical features make accurate targeting of empirical anti-MRSA antibiotics very difficult. Development of diagnostic tests capable of rapidly and accurately identifying S. aureus could greatly improve the current approach to CAP management and reduce overuse of anti-MRSA antibiotics."

This study was supported by the Centers for Disease Control and Prevention. Dr Self was supported in part by the National Institute of General Medical Sciences. One coauthor was supported in part by the National Institute on Aging. Dr Self reports receiving payment for serving on scientific advisory boards for BioFire Diagnostics and Venaxis, Inc. One coauthor reports receiving grants and nonfinancial support from MedImmune and nonfinancial support from Roche and has served as a consultant for AbbVie. One coauthor has served on a data and safety monitoring board for Novartis, and her institution has received research support from Novartis. One coauthor has served as a consultant for Pfizer Inc. The other authors have disclosed no relevant financial relationships.

Clin Infect Dis. Published online May 8, 2016. Abstract

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