Did a patient acquire legionella pneumophila from the cup filler of a dental unit or did a patient infected with l. pneumophila contaminate the cup filler?

Schonning and colleagues reported the case of a man with diagnosis of leukaemia admitted to hospital to undergo bone marrow transplantation who underwent a dental check-up and high-dose chemotherapy and developed Legionnaires’ disease in the following days. The authors entitled their case report ‘Legionellosis acquired through a dental unit’ [1]. I showed that it was not possible to confirm whether the patient acquired Legionella pneumophila from a contaminated dental unit or whether the patient, already infected with L. pneumophila, contaminated the dental unit water system.