Long term trends in the occurrence: DISCUSSION

24 Jan


Our survey demonstrates that the risk of nosocomial blood stream infections has nearly doubled for patients admitted to our hospital between 1986 and 1996, as a result of small but relentless increases from 1986 to 1995, followed by a large in­crease between 1995 and 1996. Because our surveillance tech­nique, definitions of infection and number of blood culture specimens tested did not change we believe this is a real in­crease in rate. Some of this increased rate may be only rela­tive. Hospital ‘downsizing’ has likely resulted in the out of hospital treatment of less seriously ill patients, resulting in a residual patient pool with an increased severity of illness. Despite downsizing, the actual number of nosocomial blood stream infections occurring annually in our hospital has increased, indicating that there has been an absolute as well as relative increase in risk of infection. While changes in fre­quency of nosocomial blood stream infections may not be di­rectly translatable to all nosocomial infections, these data suggest that nosocomial infections may have generally in­creased in frequency, because secondary blood stream infec­tions as a group also increased in frequency.

Our data parallel the long term trends reported from Ameri­can hospitals, but there are some important distinc­tions. Pittet et al reported that between 1981 and 1992 at the University of Iowa Hospital nosocomial blood stream in­fections increased from 6.7/1000 admissions to 18.4/1000 ad­missions compared with our average rate of 7.8/1000 and 1996 rate of 11.3/1000. They also demonstrated a linear in­crease in rate throughout the 12 survey years, both overall and for a range of specific pathogens. Our experience differs in that a slow rate of rise was seen for only coagulase-negative staphylococcal infections followed by a sudden increase in a range of pathogens in 1996. These distinctions imply that the determinants of baseline and increases in frequency of noso- comial infections, including blood stream infection, are not evenly applied among institutions, and provide justification for the collection of local as well as Canadian data, rather than simply extrapolating from the American experience. The sud­den increase that our hospital experienced in 1996 occurred after extensive restructuring of health care delivery in 1995. This occurrence will be the subject of a more in-depth study.

Our data highlight the important and growing role of intra­vascular devices as a source of nosocomial blood stream infec­tions. Over half of all the infections were attributable to a primary source, largely associated with intravascular devices. Further, the annual rate of these infections increased by 129% between 1987 and 1996, compared with a 52% increase in an­nual rate for all secondary sources; by 1996, 67% of all blood stream infections were primary. There is an urgent need for re­search into and the implementation of techniques to prevent central venous catheter infections, the most common cause of primary infections.
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Between 1986 and 1996, the rate of nosocomial blood stream infections in patients admitted to our hospital nearly doubled. This increase comprised of two patterns: a slow in­crease from 1986 to 1995, associated predominantly with coagulase-negative staphylococcal infections and primary sources, and a dramatic rise between 1995 and 1996 associ­ated with a range of pathogens.