Transregional spread of a single clone of methicillin-resistant Staphylococcus aureus between groups of drug users in Switzerland

Background: An epidemic spread of methicillin-resistant Staphylococcus aureus (MRSA) among intravenous drug users (IDUs) has been observed in Zurich. In the present study we investigated the situation in the Grisons, Switzerland. Patients and Methods: We screened IDUs and their caregivers in medical and socio-therapeutical institutions in the Grisons for MRSA. Nose swabs were used for bacterial culture and pulsed-field gel electrophoresis for MRSA genotyping. Results: A total of 191 nose swabs from ill IDUs and 80 caregivers was analyzed. None of the caregivers was MRSA positive. Six IDUs were asymptomatic MRSA carriers (5.4%). They participated in the official heroin program (MRSA prevalence in this group 16%). The MRSA genotype was identical with the single clone found in IDUs in Zurich, strongly suggesting an epidemic spread. Decolonization was successful in two persons only. Persistence of MRSA in IDUs must therefore be assumed. Conclusion: We conclude that a single clone of MRSA, found in IDUs in Zurich, has spread to a distant region of Switzerland. A rigorous infection control program in all institutions with IDUs is necessary to prevent a further spread of M RSA.