MRSA in the USA and Beyond
MRSA in the USA and Beyond
By Maria D. Mileno, MD
Dr. Mileno is Associate Professor of Medicine, Warren Alpert School of Medicine, Director, Travel Medicine, The Miriam Hospital, Providence, RI.
Dr. Mileno reports no financial relationships with companies related to this field of study.
Synopsis: Before 1975, infections due to methicillin-resistant Staphylococcus aureus (MRSA) were uncommon. Slowly but steadily, increased reporting of MRSA nosocomial infections occurred through the 1980s and '90s and now presents an additional risk for travelers.
Sources: Popovich KJ, Weinstein RA, Hota B. Are Community-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) Strains Replacing Traditional Nosocomial MRSA Strains? Clinical Infectious Diseases 2008;46;787-794.
Comparison of Both Clinical Features and Mortality Risk Associated with Bacteremia due to Community-Acquired Methicillin-Resistant Staphylococcus aureus and Methicillin-Susceptible S. aureus. Clinical Infectious Diseases 2008;46:799-806.
Boyce JM. Community-Associated Methicillin-Resistant Staphylococcus aureus as a Cause of Health Care-Associated Infection. Editorial. Clinical Infectious Diseases 2008;46:795-798.
By 1998, community-acquired (CA) cases appeared among young children and are now widely documented, representing 15-74% of Staphylococcus aureus skin and soft-tissue infections in U.S. emergency departments. Still, they had not gained great attention until the St. Louis Rams made headlines in the New England Journal of Medicine.1 Two articles and an excellent editorial in the March 15th issue of Clinical Infectious Diseases describe MRSA acquired from the community and the similarity in risk factors, outcomes, and behavior of the hospital-acquired strains.
Popovich, et al. report a method for using molecular typing methods and antimicrobial susceptibility patterns of MRSA isolates responsible for hospital-onset bloodstream infections (BSI). They classify the isolates as either community genotypes or hospital genotypes. Over a 7-year period the community genotype increased from 24% to 49%; this is significantly higher than the healthcare-associated infections reported at 16%-22% by other authors recently. There has been a statistically significant decrease in resistance to clindamycin, ciprofloxacin, and gentamicin among hospital-onset MRSA BSI isolates in parallel with an increase in number of BSI isolates showing community genotypes.
The article by Wang J, et al. examined clinical features and outcomes of adults with CA-MRSA bacteremia compared to those with CA-MSSA (methicillin-sensitive S. aureus) bacteremia in Taipei, Taiwan. Thirty patients with CA-MRSA and 185 patients with CA-MSSA infections were studied. Increased numbers of patients with CA-MRSA bacteremia were documented over time. Cutaneous abscesses and necrotizing pneumonia were independent predictors of CA-MRSA bacteremia; endovascular infection was the only independent predictor of CA-MSSA bacteremia. The same mortality rates occurred in patients with CA-MRSA as with CA-MSSA. In this cohort only 4 of the 30 patients with CA-MRSA bacteremia received empirical agents active against MRSA within the first 48 hours of hospitalization. Shock, advanced age, and thrombocytopenia were all predictors of mortality
Commentary
In summary, clone USA 300 and similar strains of virulent MRSA have taken off like wild fire on a worldwide basis. The community acquired (CA) strains have pulse field gel electrophoresis patterns that differ from hospital-acquired strains. Panton-Valentine Leukocidin (PVL), a virulence factor generated through genes that harbor staphylococcal cassette chromosome mec (sccmec) type IV or V, provides the organisms with an ability to cause necrotizing skin and soft-tissue infections including necrotizing fasciitis, as well as necrotizing pneumonia, and with the capacity to spread rapidly. Showing slight molecular differences, similarly virulent community-acquired strains are spreading in Europe, Taiwan, and Australia. Although staphylococcal infections can occur at home or abroad, it may be important to alert travelers about the risk of MRSA clone USA 300. Travelers can be warned also that necrotizing skin infections from virulent MRSA can look like spider bites, although a study of spiders concluded that house spiders do not carry MRSA.2
References
- Kazakova SV, Hageman JC, Matava M, et al. A Clone of Methicillin-Resistant Staphylococcus aureus among Professional Football Players. N Engl J Med 2005;352:5:468-475.
- Baxtrom C, Mongkolpradit T, Kasimos JN, et al. Common House Spiders are not likely Vectors of Community Acquired Methicillin Resistant Staphylococcus aureus Infections. J Med Entymology 2006:43(5):962-965.
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