Citrobacter diversus at Grace Hospital, Detroit, Michigan.

Over a six-month period from December 1973 to June 1974, isolations of Citrobacter diversus were obtained from nine patients at Grace Hospital. Our initial experience was with a patient who developed pneumonitis and a massive fatal empyema due to this organism. Seven of the nine patients were 50 years of age. Three patients had an underlying malignancy. Four patients experienced significant clinical infections. Isolations in three patients were considered to be commensal, and two isolations were of indeterminate significance. Our Citrobacter diversus isolates, which can be confused with Escherichia coli, were uniformly resistant to ampicillin and carbenicillin and sensitive to the cephalosporins, tetracyclines, and gentamicin. These results agree with previous reports. Citrobacter diversus appears to be capable of causing serious clinical disease. Patients most at risk are elderly compromised hosts and infections are usually hospital acquired.