Pseudo-outbreak of Rhizobium radiobacter Resulting from Contaminated Diluting Saline

Rhizobium radiobacter, a common environmental organism has been recognized as a rare cause of opportunistic infection in humans, usually associated with indwelling devices. We report a pseudo-outbreak of R. radiobacter infection in patients at a teaching hospital in Singapore. Eleven culture positive specimens were isolated from 9 patients from the 14th January to the 1st February, 2008. All isolates were susceptible to ampicillin, gentamicin, cotrimoxazole and ciprofloxacin. Seven patients were adult and 2 were children, with a median age of 44 years (range: 2 months 78 years). The 9 isolates from the adult patients were grown from tissue specimens collected during surgical procedures. The 2 paediatric isolates were grown from catheter tips. Patients were from 6 different orthopaedic, rheumatology, paediatric and otorhinolaryngology wards. There were 6 elective and 3 emergency procedures, 4 clean, 2 clean contaminated and 3 contaminated operations performed in 8 operating rooms by 6 different surgeons with 6 different anaesthetists. Skin preparation included povidone iodine (6), chlorhexidine (2) and alcohol (1). None of the patients were immunocompromised. None of the culture results were specifically treated and there were no documented complications on close follow-up except for one delayed surgical procedure. A review of the specimen processing techniques revealed that prior to plating, all specimens had been mixed with a commercial saline solution from a common dispenser in the microbiology laboratory. R. radiobacter was cultured from the saline from the dispenser as well as from the dispenser tip. Routine laboratory practices and precautions including autoclaving the dispenser routinely and boiling of the saline before use were resumed and the pseudo-outbreak ended. This pseudo-outbreak demonstrates the importance of prompt investigation of unusual organisms and the need for careful review of all laboratory procedures in parallel with thorough epidemiologic investigations.