Incidence, antimicrobial resistance and mortality in bloodstream infections in the critically ill

Bloodstream infections (BSI) are 7-fold more common in patients admitted to the intensive care unit (ICU) rather than to other hospital wards. The epidemiology of BSI in critically ill patients in Israel has not been systematically addressed. We examined the annual trends in BSI in patients in a general ICU of evolving patterns of antimicrobial resistance and associated mortality rates for the years 1994-1996. The presence of the systemic inflammatory response syndrome (SIRS) when the first positive blood cultures are taken was a prerequisite for its definition as clinically significant. The unit site, staff, practice guidelines, and type of patient were unchanged during the study period. Blood cultures were positive in 220.7-332.0 patients per 1000 ICU admissions, 18-22-fold more common than in regular ward patients. SIRS was a universal finding in these ICU patients. There was multi-drug resistance for the majority of species cultured, reaching 100% in some cases. Crude hospital mortality of ICU patients, with and without positive blood cultures, was 31-54% and 5-14%, respectively. The introduction of a new blood culture system (Bactec 9240) in 1996 was associated with a 61% increase in the rate of patients with positive blood cultures, accounted for mostly by increased isolation of coagulase-negative staphylococci. However the mortality rate for the latter decreased by 59%, suggesting the possibility of a selective increase in detection of contaminated cultures. Although highly prevalent in the study population and generally defining a patient group with high mortality risk, the specificity of SIRS-associated positive blood cultures may be species and culture-system dependent. These findings re-emphasize the need for both improved control measures for the epidemic proportions of BSI and multi-drug antimicrobial resistance, as well as more specific indicators of the clinical relevance of positive blood cultures in critically ill patients.