Staphylococcus aureus nasal carriage: Association with disease and HIV in a cohort of injection drug users

Injection drug users (IDU) are at increased risk of bacterial diseases such as endocarditis and abscesses; the hypothesis of this study was that this increased risk of disease could be explained by S. aureus nasal carriage (SA-NC). We conducted a prospective cohort study to evaluate prevalence and correlates of SA-NC among 571 IDUs recuited from an ongoing cohort, in Baltimore, Md. Participants completed three visits. At baseline and one month: a standardized interview, nares swab, and blood draw to assess HIV antibodies and CD4 positive T-cell levels (baseline only); at six months: interview to collect incident abscesses in prior six months. A comparison group, recruited by word of mouth from the same geographical area, received an interview and nares swab. SA-NC was determined by culture of nares swabs. SA-NC was higher among those with HIV related immunosuppression (HIV seropositive and AIDS) but was not associated with injecting drugs. Among HIV seropositives SA-NC was higher for those who reported risk behaviors potentially damaging to the nasal mucosa (nasal heroin, nasal exhalation of tobacco smoke). Antibiotic resistant strains were more common as HIV immunosuppression increased. Bactrim use was protective against SA-NC. For HIV seronegatives, eczema was correlated with SA-NC. Abscesses in the prior six months were reported by 13.4% (95% CI = 9.6% -- 18.0%). Abscesses were reported by those who may have difficulties injecting (female gender, inject in sites other than the arm, multiple venous access attempts per injection), those with poor needle hygeine (use saliva to clean skin, clean less than half the time, share needles, have itchy skin at injection site) and those with a history of abscesses and/or endocarditis. No abscesses were reported by participants using Bactrim. IHV seropositivity and SA-NC were not associated with abscesses. We reported a novel risk factor for SA-NC (nasal exhalation of tobacco smoke) but failed to show an association between SA-NC and abscesses. Instead our findings underscore the risk of injection practices and the importance of promoting skin cleaning to prevent abscesses among IDUs.