Investigation of an Epidemic of Multi-Drug Resistant Pseudomonas aeruginosa

Inter- and intrahospital epidemics of nosocomial infections due to gram-negative bacilli resistant to many antimicrobials have been well-documented. Prospective studies on the use of isolation along with epidemiologic analysis and appropriate environmental control have been lacking. In the six-month period from November 1978 to April 1979 Pseudomonas aeruginosa (MDR) resistant to all antibiotics except amikacin was isolated from 15 patients. This organism had not previously been seen in our hospital. Epidemiologic assessment of infected patients revealed that nine of 15 patients had contact either with a previously infected case or contaminated area. All strains of P. aeruginosa were identical by pyocin typing and antibiogram. The organism was present in an environmental reservoir, the urine graduated cylinder, and was found in three of eight receptacles (p = 0.002 vs. other environmental cultures). A case control study of patient risk factors showed aminoglycoside use, other antibiotic use, surgery, intravenous lines, Foley catheter use and mechanical ventilation to be no more frequent in cases than controls. The use of aminoglycosides in only 40% of cases suggests that antibiotic pressure was not the sole factor in perpetuating the epidemic.