Epidemic septic arthritis caused by Serratia marcescens and associated with a benzalkonium chloride antiseptic

During a 6-week period, 10 patients were admitted to a hospital for treatment of knee or shoulder joint infections due to Serratia species. Isolates from eight patients were identified as Serratia marcescens with identical biochemical characteristics and antibiotic susceptibility patterns. Before the onset of infections, all patients had been treated by two orthopedic surgeons who shared an office. Studies revealed that infections were associated with previous joint injections (P = 4.44 X 10(-5] of methylprednisolone and lidocaine. Environmental cultures revealed that a canister of cotton balls soaked in aqueous benzalkonium chloride and two multiple-dose vials of methylprednisolone previously used by office personnel were contaminated with the epidemic strain of S. marcescens. The canister may have served as a potential reservoir for contamination of sterile solutions and equipment used for joint injections, of skin at the injection site, and of hands of personnel. No further cases occurred after the use of aqueous benzalkonium chloride was discontinued.