Online Program

Unraveling an outbreak of methicillin-resistant staphylococcus aureus in a neonatal intensive care unit utilizing genomic epidemiology

Sunday, November 3, 2013

Taj Azarian, MPH, Epidemiology Department, University of Florida, Gainesville, FL
Robert L. Cook, MD, MPH, College of Public Health and Health Professions, Department of Epidemiology, University of Florida, Gainesville, FL
Judy Johnson, PhD, Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL
Marco Salemi, PhD, Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL
Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of healthcare-associated infections, and a significant contributor to healthcare costs globally. Current molecular-typing methods lack the discriminatory resolution to discern outbreaks from sporadic cases of these highly clonal bacteria.

During a 12 month period, 34 cases of MRSA were identified among patients in a neonatal intensive care unit of a Florida hospital. Of these, 17 isolates were identified by PFGE analysis as type USA300 and further investigated as the “outbreak strain”. Despite an extensive investigation, no clear etiology was established. The utilization of whole genome sequencing (WGS) and phylogenetics would provide the resolution required to further differentiate between outbreak and sporadic cases.

Methods: To elucidate the outbreak etiology, we retrospectively obtained the 17 USA300 isolates and corresponding epidemiological data. Spa-typing was utilized to provide the next level of molecular resolution. We subsequently applied WGS and phylogenetic analysis in the context of epidemiological data to further resolve the transmission dynamics of the outbreak.

Results: We identified 12 isolates that were spa-type t008, two t118, two t211, and one t5593. Based on calculated genetic distances, the t118 isolates were likely unrelated to the primary outbreak and the t211 isolates may represent a sub-epidemic.

Conclusion: Our analysis demonstrated that phylogenetic analysis can discriminate pathogen strains and can be used in conjunction with epidemiological data during outbreaks to identify potential etiologies. Phylogenetic investigation furthers our ability to track pathogen emergence, investigate outbreaks, and develop targeted control measures, ultimately reducing morbidity and mortality from these organisms.

Learning Areas:

Protection of the public in relation to communicable diseases including prevention or control
Public health biology

Learning Objectives:
Analyze an outbreak of Methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit by applying advancements in whole genome sequencing and phylodynamics. Identify the potential etiology of the epidemic by discriminating between genetically similar yet epidemiologically distinct strains of MRSA in combination with clinical and epidemiological data.

Keyword(s): Infectious Diseases, Hospitals

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: I am currently a PhD student in the Department of Epidemiology at the University of Florida. My current research involves phylogenetics of bacterial and viral pathogens as well as infectious disease epidemiology and antibiotic resistance. I am a previous fellow of the Florida Department of Health and have completed several outbreak investigations within the healthcare setting. I have also been heavily involved in the work of my mentors and their publications.
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.