Nosocomial bloodstream infections (BSIs) are important causes of morbidity and mortality
in the United States.
Data from a nationwide, concurrent surveillance study (Surveillance and Control of
Pathogens of Epidemiological Importance [SCOPE]) were used to examine the secular
trends in the epidemiology and microbiology of nosocomial BSIs.
Our study detected 24,179 cases of nosocomial BSI in 49 US hospitals over a 7-year
period from March 1995 through September 2002 (60 cases per 10,000 hospital admissions).
Eighty-seven percent of BSIs were monomicrobial. Gram-positive organisms caused 65%
of these BSIs, gram-negative organisms caused 25%, and fungi caused 9.5%. The crude
mortality rate was 27%. The most-common organisms causing BSIs were coagulase-negative
staphylococci (CoNS) (31% of isolates), Staphylococcus aureus (20%), enterococci (9%),
and Candida species (9%). The mean interval between admission and infection was 13
days for infection with Escherichia coli, 16 days for S. aureus, 22 days for Candida
species and Klebsiella species, 23 days for enterococci, and 26 days for Acinetobacter
species. CoNS, Pseudomonas species, Enterobacter species, Serratia species, and Acinetobacter
species were more likely to cause infections in patients in intensive care units (P<.001).
In neutropenic patients, infections with Candida species, enterococci, and viridans
group streptococci were significantly more common. The proportion of S. aureus isolates
with methicillin resistance increased from 22% in 1995 to 57% in 2001 (P<.001, trend
analysis). Vancomycin resistance was seen in 2% of Enterococcus faecalis isolates
and in 60% of Enterococcus faecium isolates.
In this study, one of the largest multicenter studies performed to date, we found
that the proportion of nosocomial BSIs due to antibiotic-resistant organisms is increasing
in US hospitals.