Incidence of and factors associated with methicillin-resistant Staphylococcus aureus skin and soft-tissue infections among HIV-infected persons

OF THE THESIS Incidence of and Factors Associated with Methicillin-Resistant Staphylococcus aureus Skin and Soft-Tissue Infections among HIV-Infected Persons by Aladdin H. Shadyab Master of Science in Bioinformatics and Medical Informatics San Diego State University, 2012 Background: Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are an important cause of morbidity and have become an important public health threat throughout the past decade. Persons infected with human immunodeficiency virus (HIV) have an increased risk for MRSA infections compared to the general population, and a 6-18 fold increase in risk has been reported. Limited studies have examined recent trends in the incidence of MRSA skin and soft-tissue infections (SSTIs) among HIV-infected persons, with one suggesting that the incidence is now declining. Furthermore, factors associated with the development of initial and recurrent MRSA SSTIs have not been fully elucidated among HIV-infected persons. It is currently not known whether specific treatment approaches for the initial MRSA infection reduce the risk for recurrent infection. An understanding of the epidemiology of and the factors associated with MRSA SSTIs is imperative for prevention of MRSA infections. Purpose: The purpose of this study is to examine recent trends in the incidence of MRSA SSTIs and to determine factors associated with the development of initial and recurrent MRSA SSTIs. Methods: We retrospectively evaluated a large cohort of HIV-infected military beneficiaries from 1993-2010 for wound culture-proven MRSA SSTIs. Multiple logistic regression models evaluated factors associated with MRSA SSTIs. Linear mixed-effects models assessed the impact of CD4 cell count and HIV viral load measurements on the development of recurrent infections. Finally, the random forests algorithm determined variables most predictive of initial and recurrent MRSA SSTIs. Results: Of 794 patients, 63 (8%) experienced a total of 108 MRSA SSTIs from 1993-2010 for an incidence of 19.3 infections/1000 person-years. A 2.4-fold increase in the incidence was observed from 2003-2006 (p< 0.01); however, a decreasing trend in the incidence was noted from 2007-2010. Factors associated with initial MRSA SSTIs included a CD4 cell count <500 cells/mm3 and HIV viral load ≥400 copies/mL (OR 5.2; p-value <0.01), CDC stage C (OR 5.4; p-value <0.01), and injection drug use (OR 4.9; p<0.01). Factors associated with recurrent MRSA SSTIs included hospital admission after the initial infection (OR 7.4; p=0.02). Minocycline for treatment of the initial infection was associated with an 80% reduction in the odds for recurrence (OR 0.2; p=0.03). In the linear mixed model, patients who experienced a recurrent infection had on average lower CD4 cell counts than patients who did not experience recurrence (p=0.03). Variables associated with poor immune status were most predictive of initial and recurrent infections in the random forests analysis. Conclusion: HIV-infected persons with poor immune status may be immunologically predisposed to develop MRSA SSTIs. Minocycline for treatment of MRSA SSTIs may