A nosocomial outbreak of Ralstonia mannitolilytica linked to cosmetic water mist sprays in the intensive care unit of a tertiary care hospital, Switzerland, 2024

<i>Ralstonia mannitolilytica</i> is a rare emerging, multidrug-resistant, opportunistic pathogen known to cause nosocomial outbreaks associated with hospital water sources and medical devices. In June 2024, the microbiology laboratory of Lausanne University Hospital alerted the Infection Prevention and Control Unit following the detection of <i>R. mannitolilytica</i> in clinical samples from two intensive care unit (ICU) patients. This triggered a comprehensive epidemiological investigation, including extensive environmental sampling and whole genome sequencing of the isolates. Between May and June 2024, <i>R. mannitolilytica</i> was detected in three ICU patients. Activation of the Swissnoso network led to the identification of an additional case in a rehabilitation centre. Environmental investigations traced the source to commercial cosmetic water mist sprays used for patient care. The sequences confirmed a genetic match between patient and spray isolates, prompting the immediate withdrawal of this product. This nosocomial outbreak of <i>R. mannitolilytica</i> revealed an unexpected and seemingly innocuous source of contamination - water mist sprays - highlighting the importance of considering cosmetics products used in patient care and questioning their use in patients with risk factors, such as those in ICU or with immunosuppression.