Exogenous or endogenous reservoirs of nosocomialPseudomonas aeruginosa andStaphylococcus aureus infections in a surgical intensive care unit

Objective A 4 month prospective study was performed to assess the incidence and routes of endogenous or exogenous colonization and nosocomial infection caused byStaphylococcus aureus andPseudomonas aeruginosa in surgical critically ill patients.Design A total of 4634 specimens ware obtained. Patient's nasal, scalp, and rectal swabs as well as tracheal secretion (TS) were cultured every second day beginning on the day of admission. Nasal swabs and hand cultures of the personnel as well as cultures from gowns were also taken. all isolates ofS. aureus were phage typed and 116 of these isolates were also plasmid typed.P. aeruginosa isolates were sero-and pyocin typed. Resistance patterns were determined in all isolates.Setting The suty was carried out in the surgical intensive care unit (SICU) of an teaching hospital.Patients During the study period each patient (a total of 153 patients) admitted to the SICU entered the study.Results P. aeruginosa andS. aureus colonisation rate on admission were 5% and 36.5% respectively. Only 10 patients (6.5%) were colonized withP. aeruginosa during hospitalization, and only 7 patients (4.5%) acquiredS. aureus in the surgical intensive care unit (SICU). The most common primary colonisation site ofP. aeruginosa was the rectum, whereasS. aureus was predominantly found in nasal cultures. Horizontal transmission ofS. aureus occured in only 2 patients.Conclusion The study suggests that colonisation withP. aeruginosa andS. aureus occurs from endogenous rather than from exogenous sources and that the endogenous acquisition of both bacteria play a more important role in development of nosocomial infections than the exogenous route of transmission.