Household Colonization of MRSA: A Problem that Lingers for Years

Methicillin-resistant Staphylococcus aureus (MRSA) has proven to be a unique and challenging organism to both manage with infection control strategies and treat pharmacologically. The organism was originally identified as a transmittable vector from primarily healthcare facilities but over time has also evolved into a community-acquired organism. Since the 1990s, the organism has been identified within the community and has evolved into various genotype clone variation. One such clone variation is the USA300, which is a particularly virulent and easily transmissible organism associated with skin infections and also has been associated with necrotizing pneumonia and endocarditis.

Researchers from Emory University and the University of Chicago used a study published in 2012 in the Journal of Clinical Infectious Disease, which looked at 146 USA300 MRSA isolates from 2008 to 2010. Skin structure infections and colonization cultures from 21 households from Chicago and Los Angeles were included in the analysis. Among 1,162 patients (350 skin infection patients and 812 household members) Staphylococcus aureus colonized one or more body sites 40% (137 of 350) of patients with skin infections and 50% (405 of 812) of their household contacts.¹

For the current study, investigators evaluated the samples to understand transmission dynamics, genetic relatedness and microevolution of USA300 MRSA within the households. The researchers found that isolates within households clustered into closely related groups which were suggestive of a single USA300 strain was introduced and transmitted within each household. Researchers identified that USA300 MRSA persisted within households from 2.3 to 8.3 years before their sample was collected and the USA300 clones continued to acquire extraneous DNA. Also, the findings suggested that unique USA300 MRSA isolates are transmitted within households that contain a single individual with a skin infection. Dr. Michael Z. David, one of the researchers stated “although MRSA is introduced into households rarely, once it gets in, it can hang out there for years, ping-ponging around from person to person.”²  Based on this startling data we must also focus not only on the patient treated with MRSA but also the decolonization of household members may be critical component to prevent the transmission of USA300 MRSA in the United States.

Pharmacists are increasingly utilized for their infectious disease experience, including taking active roles in antibiotic stewardship and surveillance programs. Since household members are vectors for MRSA transmission, do you see a future role for pharmacists in community-based infection control practices including antibiotic surveillance?  All comments are welcome.

Michael J. Cawley, PharmD, RRT, CPFT, FCCM, is a Professor of Clinical Pharmacy at the Philadelphia College of Pharmacy, University of the Sciences. He has greater than 25 years of experience practicing in the areas of medical, surgical, trauma, and burn intensive care as both a critical care clinical pharmacist and registered respiratory therapist.

References:

1. Alam MT, Read TD, Petit RA 3^rd, et al. Transmission and microevolution of USA300 MRSA in U.S. households: evidence from whole-genome sequencing. MBio. 2015;6(2):e00054-15.

2. MRSA can linger in homes, spreading among its inhabitants. News-Line for Healthcare Providers. www.news-line.com. Accessed March 19, 2015.