An increasing number of Pseudomonas species have been implicated in bacteremia.Įnterobacter bacteremia has also been caused by contaminated blood products, but Enterobacter is reported to contaminate IV fluids more frequently. Pseudomonas fluorescens has caused bacteremia in association with blood transfusion. Pseudomonas cepacia has also caused an increasing incidence of bacteremia and outbreaks associated with hospital devices, such as a blood gas analyzer. Isolates can be cultured from the hospital environment, and common-source outbreaks can occur. For example, Xanthomonas maltophilia (formerly Pseudomonas maltophilia) infection has been increasing because of the aminoglycoside resistance of this organism. The pattern of gram-negative bacteremia has been changing with the introduction of new antimicrobials. Bacteroides bacteremia suggests anaerobic infection of the colon or female genital tract, a liver abscess, or postoperative wound infection. aeruginosa are much more common than Proteus species, Providencia, or even E. In bacteremic pneumonia, Klebsiella pneumoniae and P. For example, Proteus mirabilis or Providencia species isolated from blood cultures suggest urinary tract infection. The site of infection may also predict the etiologic agent. Some organisms, such as Acinetobacter species, may be common in one hospital and unusual in another. Each hospital has its own profile of etiologic agents. coli is by far the most common agent in the healthy young patient. aeruginosa is more likely to occur in the neutropenic patient, whereas E. The population studied will also affect the distribution of etiologic agents in gram-negative bacteremia. The longer the length of stay, the more likely it is that these relatively antimicrobial-resistant organisms will be found. Organisms such as Pseudomonas aeruginosa and Serratia marcescens are most likely to occur in the hospital. If the bacteremia is acquired in the community, E. The gram-negative organism most likely to cause bacteremia varies with several factors. Primary sources of gram-negative bacteremia Etiologic agents in gram-negative bacteremia The respiratory tract (i.e., bacteremic pneumonia) was the source in only 9% of cases, and skin and soft tissue in 6.5%. Urinary tract infection is by far the most common source, with infection of the gastrointestinal and biliary tract second. Table 68-2 shows the sources of gram-negative bacteremia. Escherichia coli was the most common gram-negative rod causing bacteremia, being responsible for 31% of cases. Table 68-1 shows the distribution of etiologic agents. Kreger and associates, for example, reviewed 612 episodes of gram-negative bacteremia during a 10-year period. Several studies have classified gram-negative bacteremia according to most common etiologic agent and most frequent source of infection. Specific identification of the gram-negative bacillus will also sometimes be helpful in identifying a primary infection. The history and physical examination will usually strongly suggest the source of infection. When the microbiology laboratory reports that a blood culture is positive for a gramnegative bacillus, it must be assumed that the patient is bacteremic and a life-threatening infection is present. LABORATORY REPORT OF A GRAM-NEGATIVE ROD IN THE BLOOD
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