Staphylococcus aureus carriage and prevalence of skin and soft tissue infections among people who inject drugs: a longitudinal study.

People who inject drugs are frequently colonized with Staphylococcus aureus and have an increased risk for skin and soft tissue infections. This longitudinal study aims to describe S. aureus carriage in this group and the risk for infections during a 1-year follow-up. We included 61 participants from the Malmö Needle Exchange Program. Mapping of S. aureus carriage was conducted by screening cultures every third month and S. aureus growth was semi-quantified. Data regarding infections and living conditions were collected from structured interviews. Statistics included univariate analysis with the Fischer's exact test, univariate logistic regression and multivariate logistic regression. S. aureus carriage was detected in 46-63% of participants, and 75% reported one or more infections during the study period. Self-reported infections were associated with carriage in perineum (OR 5.08 [95% CI 1.45-17.73]), in skin lesions (OR 1.48 [95% CI 1.21-1.81]), and unstable housing situation (OR 12.83 [95% CI 1.56-105.81]). Thus, people who inject drugs are frequent carriers of S. aureus and report a surprisingly high prevalence of skin and soft tissue infections. Homeless people and those with skin carriage seem to be at highest risk. Effective clinical interventions are needed, aiming at preventing infections in this vulnerable group.