Noah D. Cohen, VMD, MPH, PhD, DACVIM (large animal)

The epidemiology of R. equi remains ill-defined and continues to evolve. Two epidemiologic questions of clinical importance regarding Rhodococcus equi foal pneumonia are "Why are some foals affected while others in the same environment remain unaffected?", and "Why does the disease occur recurrently at some farms but not at others?". To answer these questions, studies performed at the level of the foal and farm, respectively, are needed.

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) as a major human health concern has heightened awareness of the occurrence of this agent in companion animals, including horses. The purpose of this presentation is to review what basic knowledge equine practitioners should have regarding MRSA and other methicillin-resistant staphylococcal species in horses.

The principles of evidence-based medicine (EBM) were first developed by clinical epidemiologists during the late 1980s. EBM has been described as "the integration of the best research evidence with our clinical expertise and our patient's unique values and circumstances".

The gold-standard for diagnosis of Rhodococcus equi pneumonia is isolation of the organism from fluid obtained by tracheobronchial aspiration (TBA) from a foal with clinical signs of pneumonia, preferably accompanied by cytologic evidence of sepsis, sonographic or radiographic evidence of pneumonia, or both.

Critical appraisal of reports entails 3 fundamental steps: 1) determining if study results are valid; 2) assessing the clinical importance of study findings; and, 3) assessing if the results of valid, clinically important studies are relevant to our patients. A foundation for applying these 3 steps is a hierarchy of study types for EBM, which places a premium on those that are patient-based. Clinical importance has many interpretations, but in terms of quantification it is best assessed in reference to the magnitude of the observed association(s) in a study.

Among equids, R. equi infections occur almost exclusively among foaIs; infected adult horses generally have an underlying immunodeficiency, and human cases of R. equi are most commonly reported among persons infected with HIV or with other forms of immunosuppression such as that induced by drugs in transplant recipients and those receiving chemotherapy.