Ralstonia mannitolilytica is a non-fermentative, gram-negative bacterium isolated infrequently from clinical samples. However, within a period of 11 weeks five inpatients of the tertiary care hospital of the University of Tübingen developed clinical signs of infection and R. mannitolilytica was cultivated from blood samples of all patients suggesting an outbreak.Blood cultures and one catheter tip were analysed by standard microbiological procedures. Genetic relatedness of the isolates was investigated by pulsed-field gel electrophoresis. To ascertain the possible source of the outbreak, environmental sampling and challenge-recovery experiments to test filters used for multi-dose solution bottles were performed.In the present study a monoclonal outbreak with R. mannitolilytica causing catheter-related infection of five haematological patients is reported. Underlying severe diseases with consecutive immunosuppression, permanent indwelling intravenous devices, multiple intravenous applications, and chemotherapy were possible risk factors promoting the infection. Challenge-recovery experiments revealed that R. mannitolilytica to a high extent even passed through Mini-spike Plus filters of pore size 0.2 microm.Although the source of the outbreak could not be identified, it is possible that solutions given intravenously were contaminated. Since R. mannitolilytica had never been isolated in our laboratory before and environmental testings performed were negative, it cannot be excluded that commercial products like drugs, saline solutions or infusion systems (filters) were contaminated.