Long term trends in the occurrence: METHODS

22 Jan

The University of Alberta Hospital is a tertiary acute care facility and principal teaching hospital of the University of Al­berta Faculty of Medicine. All forms of acute medical care were provided during most of the survey period, including adult and paediatric medicine and surgery, obstetrics/gynecology, hematological oncology, and solid organ transplantation. The hospital has seven intensive care units (ICUs) for critically ill patients: cardiac, adult medical surgical, cardiac surgery, burns, neurosurgery, pediatric and neonatal. In 1995, as part of health care reorganization in the region, all inpatient ob- stetrics/gynecology, and ophthalmology were transferred to another facility, and increased services were created for inten­sive care, neurosurgery and cardiac surgery. In 1986, at the beginning of the survey, there were approximately 1200 inpa­tients beds. Through the study period, there was a gradual re­duction in bed number, reaching 1000 in 1992, followed by an abrupt decline from 1992 to 1994, stabilizing at about 600.

Average admissions remained stable at about 2500/month be­tween 1986 and 1993. Beginning in 1994, a gradual decline in admissions occurred, to 1980 per month in 1996. Annual blood culture specimens processed by the hospitals clinical microbiology laboratory remained stable through the study period (10,000 to 12,000 specimens per year, R Rennie, per­sonal communication).

Other than in ICUs, where phlebotomy was performed by registered nurses, blood cultures were obtained by physicians. Blood cultures were typically performed in sets of two, and in­cubated aerobically and anaerobically for five to seven days (unless prolonged incubation was requested). Blood cultures reported as growing microorganisms were reviewed daily by nurse practitioners in the hospital’s Infection Control pro­gram. Patient charts were reviewed. The isolate was classified as a contaminant or as resulting from community-acquired or nosocomial infection based on Centers for Disease Control and Prevention (CDC) criteria. When an organism isolated from blood culture was compatible with a nosocomial infec­tion at another site, the blood stream infection was classified as secondary to that other infection. Other isolates, including all intravascular device related infections were classified as primary. When the isolate was an organism that was normal skin flora (eg, coagulase negative staphylococci, Bacillus spe­cies, Propionibacterium species), it was considered significant if there were clinical symptoms present, and either the organ­ism was isolated from at least two separate blood cultures or a physician instituted appropriate antimicrobial therapy. The source of secondary infection was determined by chart review. The service or ward where the patient was located when the signs or symptoms of infection first developed was recorded. All cases included in the database occurring between August 1, 1986, the initiation of the surveillance program, and Decem­ber 31, 1996 were reviewed.

Data management and statistical methods: Cases of noso- comial blood stream infection were entered into Automated In­fection Control Expert (Infections Control and Prevention Analysts Inc, Austin, Texas), a computer software program de­signed for nosocomial infection surveillance. Statistical com­parison of rates was performed by EPI INFO, version 6.04b (CDC, Atlanta, Georgia). P<0.05 was considered significant.
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