Abstract: A system for treating and/or preventing a viral, bacterial and/or fungal infection in the oral cavity and/or along the respiratory tract, in particular the interior of the nose, throat, trachea and/or lungs, of a patient by reactive species generated by plasma as well as a plasma for such use is disclosed. The system comprises a plasma source generating reactive species in a gas, the plasma source being configured to be located outside a body of the patient, and a species directing member forming at least one duct for guiding at least a part of the reactive species generated by the plasma source into the oral cavity and/or the respiratory tract.