Nasal carriage of inducible dormant and community-associated methicillin-resistant Staphylococcus aureus in an ambulatory population of predominantly university students

Background: We studied risk factors for nasal colonization with inducible dormant methicillin-resistant Staphylococcus aureus (ID-MRSA) and community-associated MRSA (CA-MRSA) in a cohort of predominantly university students. Methods: Nasal surveillance cultures were performed in student health and ambulatory clinics. Molecular features were identified and risk factors for CA-MRSA and ID-MRSA colonization were determined by logistic regression. Results: Of the 1000 participants, 89% (n = 890) were university students. Sixty-four percent were female, 59% Caucasian. The mean age was 23.5 years; 1.6% (n = 16) were CA-MRSA and 1.4% (n = 14) were ID-MRSA colonized. Fifteen (94%) of the CA-MRSA strains were PFGE type IV. pvl (Panton-Valentine leukocidin gene) positivity was 75% in CA-MRSA and 57% in ID-MRSA. ID-MRSA isolates were pulsed-field gel electrophoresis (PFGE) type I, 7%; type II, 14%; type V, 7%; and type IV, 71%. CA-MRSA SCC. mec classification was 94% type IV and 6% type V. Risk factors for carriage of CA-MRSA were older age (OR 1.046, p= 0.040) and dog ownership (OR 1.450, p= 0.019). Single family home (OR 0.040, p= 0.007) was a protective factor. There were no significant variables of association found for ID-MRSA colonization. Conclusions: ID-MRSA/CA-MRSA colonization was low. Most isolates were PFGE types IV and II, pvl-positive and susceptible to several antibiotics. Older age and dog ownership were risk factors for CA-MRSA. Future studies are needed to assess the impact of ID-MRSA carriage.