Community-Associated MRSA and MSSA: Clinical and Epidemiologic Characteristics
Miller LG, Perdreau-Remington F, Bayer AS, et al. Clinical and epidemiologic characteristics cannot distinguish community-associated methicillin-resistant Staphylococcus aureus infection from methicillin-susceptible S. aureus infection: a prospective investigation. Clin Infect Dis. 2007 Feb 15;44(4):471-482. Epub 2007 Jan 19.
Methicillin-susceptible Staphylococcus aureus (MSSA) was, until very recently, the predominant strain seen in community-associated (CA) S. aureus infections. Now methicillin-resistant S aureus (MRSA) is a concern around the world. Deciding whether or not to treat empirically for MRSA in those patients who do not have risk factors for healthcare-associated (HCA) infections is difficult.
Investigators at the University of California-Los Angeles Medical Center (Torrance) prospectively evaluated consecutive patients admitted to the county hospital with S. aureus infections. Daily cultures of wounds, urine, blood, and sputum were taken. An extensive questionnaire was completed by 280 patients who provided information on exposures, demographic characteristics, and clinical characteristics. CA infections were defined as those not having a positive culture from a surgical site in a patient who, in the past year, had not lived in an extended living facility, had any indwelling devices, visited an infusion center, or received dialysis.
Of those evaluated, 202 patients (78%) had CA S. aureus and 78 (28%) had HCA S. aureus. Of those with the CA infections, 108 (60%) had MRSA and 72 (40%) had MSSA. Sensitivity, specificity, predictive values, and likelihood ratios for the risk factors evaluated were unable to distinguish CA-MRSA from CA-MSSA. For example, the sensitivities for most MRSA risk factors were less than 30%, and all the positive likelihood ratios were lower than three.
This study has very important consequences. Given the data presented, there is currently no way to consistently distinguish between CA-MRSA and CA-MSSA prior to culture results. It would be very reasonable in this population to treat for MRSA empirically. One limitation is that the information comes from a single center in an area that has a very diverse patient population. Also, because this was done at a county hospital, the resources for treating patients who would be cared for in the outpatient arena at other centers might not otherwise be available, thus generalizing this data to potential outpatients. Because the morbidity and mortality from a delay in treatment of MRSA infections is significant, however, it appears sensible to treat CA S. aureus empirically in areas where CA-MRSA is common, regardless of patients’ risk factors.
Venous Thromboembolism Update
King CS, Holley AB, Jackson JL, et al. Twice vs three times daily heparin dosing for thromboembolism prophylaxis in the general medical population: a metaanalysis. Chest. 2007 Feb;131(2):507-516.
Nijkeuter M, Sohne M, Tick LW, et al. The natural course of hemodynamically stable pulmonary embolism: clinical outcome and risk factors in a large prospective cohort study. Chest. 2007 Feb;131(2):517-523.
Segal JB, Streiff MB, Hoffman LV, et al. Management of venous thromboembolism: a systematic review for a practice guideline. Ann Intern Med. 2007 Feb 6;146(3):211-222.
Snow V, Qaseem A, Barry P, et al. Management of venous thromboembolism: a clinical practice guideline from the American College of Physicians and the American Academy of Family Physicians. Ann Intern Med. 2007 Feb 6;146 (3):204-210. Epub 2007 Jan 29.
The prevention and treatment of venous thromboembolism (VTE) is a skill set required for all hospitalists given the prevalence of this condition in hospitalized patients as well as the significant morbidity and mortality associated with the condition. Several articles that help to guide our decisions in managing VTE have been published recently.