Participant Selection

This study population was derived from a longitudinal study and consisted of 14 participants, all of whom were colonized with S. aureus: 3 pediatric index patients with cutaneous or invasive CA-MRSA infections and 11 healthy household contacts of these patients. The cohort was recruited from Saint Louis Children’s Hospital and community pediatric practices as described previously.¹³ At enrollment, swabs (Eswab, Becton Dickinson [BD], Franklin Lakes, NJ) were collected for culture from the anterior nares, axillae, and inguinal folds of each participant to determine S. aureus colonization status. In the present study, S. aureus isolates recovered from the same niche (i.e. the axillae, inguinal folds, or anterior nares) of 14 participants (designated A-N) were evaluated for polyclonality as described below. This study was approved by the Washington University School of Medicine Human Research Protection Office. Written informed consent was obtained from all participants.