Objectives: Identification of patterns of S. aureus colonization and spread among active drug users and their contact networks over time.

Methods: Snowball sampling is used to recruit subjects from a population of current drug users in a low-income, predominantly African-American/black neighborhood in New York City. A coupon system facilitates and tracks secondary recruitment of named network members and additional contacts that share social and/or drug use settings. Social network methodology describes an array of potential risk relationships for S. aureus transmission. Participant linkages are defined by a combination of geographic, temporal, sexual, and drug use partnerships. Nasal and paraphernalia cultures as well as cultures of sites of infection for S. aureus are used to assess the prevalence of colonization and to characterize molecularly distinct isolates of S. aureus. Related S. aureus isolates are defined by molecular fingerprinting and these isolates are then compared to social and risk networks.

Results: Ninety-three primary participants with 212 secondary recruits have been enrolled using the coupon system. Of these 305 participants, 69% have used crack, 44% have used cocaine, 66% have used heroin and 25% have injected in the 6 months prior to interview.  14% are HIV positive.  Of the 250 nasal swabs tested to date for the presence of S. aureus 39 (15.6%) are positive.

Conclusions: These techniques represent a method for study of transmission of S. aureus within high risk groups.  This approach can be applied to recruit hard to reach populations and to describe and characterize transmission of infectious diseases within networks and in communities.