Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterial pathogen that leads to an increase in morbidity and mortality. To decrease the spread of MRSA, there is a need to elucidate factors that lead to patient-to-patient transmission in critical care settings. Objectives:
Aim 1: To understand if patient-to-patient transmission via HCP mediator differs between high-risk activities by determining the odds of MRSA contamination of the patient from the gown and gloves of the health care personnel (HCP).

Aim 2: To determine if isolates found on the gown and gloves of HCP are similar to patient isolates after performing an HCP-patient interaction, using comparative genomic techniques.

Methods:
Aim 1: This was an observational study of MRSA-positive patients and the HCP who cared for them. We conducted a simulation study of patient-to-patient transmission of MRSA from a HCP vector to a manikin (proxy for the subsequent patient). Using a generalized linear mixed model, we determined the odds of manikin contamination after performing HCP-patient interactions.

Aim 2: We selected 95 patient MRSA isolates and their co-isolated HCP gown or glove MRSA isolates using a stratified sampling method. Comparative genomics analyses such as phylogenetic analysis, spa-typing, multi-locus sequence typing (MLST), large-scale blast score ratio (LSBSR), and single nucleotide variant (SNV) analysis were used to achieve this aim’s objective. Results: Aim 1: We observed 103 HCP-patient interactions with 65 MRSA-positive patients and found that subsequent transmission of MRSA from HCP gown and gloves to the manikin proxy occurred 10.7% of the time. There was no association between high-contact patient care activities and MRSA contamination of the manikin following patient care activity (p-value=0.1).

Aim 2: Using multiple typing methods, we found that the majority of our isolates were genetically similar. The phylogenetic analysis revealed that 85.2% of paired isolates were similar, and the spa-typing and the LSBSR found that more than 75% of our paired isolates were concordant. However, SNV and MLST identified more than 40% of our paired isolates as discordant.

Conclusion: The studies conducted demonstrated patient-to-patient transmission of MRSA via HCP vector, indicating the importance of contact precautions and infection control practices.