Methicillin Resistant Staphylococcus aureus (MRSA) Prevalence in a Residents' Population

Background: Working with patients is a known risk factor for methicillin resistant Staphylococcus aureus (MRSA) acquisition.  Residents are at risk of contracting MRSA considering their repeated contacts with patients during their training.  There are yet no available data on residents’ MRSA colonization rate.  Furthermore, there are no data on MRSA carriage in healthcare professionals in the province of Québec.

Objective: Determine MRSA carriage rate in Laval University residents and compare it to the MRSA carriage rate of a control group (undergraduate medicine students with no previous patients contacts).

Methods: Participants were recruited during their regular academic activities. They filled a questionnaire about relevant risk factors and demographic data. All data were anonymous.

After informed consent was obtained, participants were screened for MRSA carriage with a nasal swab in both anterior nares. An enrichment broth (BHI) was first inoculated and incubated 24 hours. A MRSA select BIORAD agar was then inoculated from the broth and incubated another 24 hours before reading. Pink colonies were confirmed as MRSA with antibiotic susceptibilities testing by Clinical and Laboratory Standards Institute (CLSI) standards and penicillin binding protein 2A detection.

Recruitment goal was set at 250 participants in each group, considering a 0,0% prevalence in the control group and a 4,5% increase in the study group as significant and accepting β and α errors of 0,2 and 0,05 respectively.

Results: 250 residents of all residency levels from medical and surgical programs and 247 controls were recruited between February and April 2010. One case of MRSA carriage was detected in the residents group and none in the control group (prevalence of 0,4% vs. 0,0%, p=1,00).  The only case had an antibiotic susceptibilities profile of a hospital MRSA, considering that community-acquired MRSA in Quebec City are usually sensitive to clindamycine.  His risk factors were dermatitis and antibiotics use in the past three months.

Conclusions: Residents in Quebec City appear at very low risk of contracting MRSA through their professional exposition. This may reflect the decreasing rate of healthcare-associated MRSA in Quebec City.  Good health and young age may also play a role: residents may eliminate promptly MRSA when in contact with it instead of becoming colonized.  Laval university teaching hospitals strict infection control policies for MRSA patients (including cohorting, gloves, gown and patient-dedicated equipment) may also contribute to prevent MRSA transmission.