To assess changes since the mid-1970s, we reviewed 843 episodes of positive blood cultures in 707 patients with septicemia. The five most common pathogens were Staphylococcus aureus, Escherichia coli, coagulase-negative staphylococci (CNS), Klebsiella pneumoniae, and Enterococcus species. Although CNS were isolated most often, only 12.4% were clinically significant. Half of all episodes were nosocomial, and a quarter had no recognized source. Leading identifiable sources included intravenous catheters, the respiratory and genitourinary tracts, and intraabdominal foci. Septicemia-associated mortality was 17.5%. Patients who received appropriate antimicrobial therapy throughout the course of infection had the lowest mortality (13.3%). Multivariate analysis showed that age (relative risk [RR], 1.80), microorganism (RR, 2.27), source of infection (RR, 2.86), predisposing factors (RR, 1.98), blood pressure (RR, 2.29), body temperature (RR, 2.04), and therapy (RR, 2.72) independently influenced outcome. Bloodstream infections in the 1990s are notable for the increased importance of CNS as both contaminants and pathogens, the proportionate increase in fungi and decrease in anaerobes as pathogens, the emergence of Mycobacterium avium complex as an important cause of bacteremia in patients with advanced human immunodeficiency virus infection, and the reduction in mortality associated with infection.

The presence of microorganisms in a patient's blood is a critical determinant of the severity of the patient's illness. Equally important, the laboratory isolation and identification of a microorganism present in blood determine the etiologic agent of infection, especially when the site of infection is localized and difficult to access. This review addresses the pathophysiology and clinical characteristics of bacteremia, fungemia, and sepsis; diagnostic strategies and critical factors in the detection of positive blood cultures; characteristics of manual and instrument approaches to bacteremia detection; approaches for isolating specific microorganisms associated with positive blood cultures; and rapid methods for the identification of microorganisms in blood cultures.

In a collaborative study at three university hospitals, the recovery of microorganisms and the speed of detection of microbial growth by the BacT/Alert (Organon Teknika Corporation, Durham, N.C.) and BACTEC 660/730 (Becton-Dickinson Diagnostic Instrument Systems, Sparks, Md.) nonradiometric blood culture systems were compared. A total of 5,918 comparisons were made between BacT/Alert aerobic and BACTEC NR 6A bottles and 5,992 comparisons were made between BacT/Alert anaerobic and BACTEC NR 7A bottles. Each bottle was inoculated with 5 ml of blood. The overall recoveries of microorganisms from the two aerobic bottles were comparable; members of the family Enterobacteriaceae were recovered more often from BacT/Alert aerobic bottles alone (P < 0.001). The overall recoveries of microorganisms from the two anaerobic bottles were not significantly different. Growth of Staphylococcus aureus (P < 0.001), coagulasenegative staphylococci (P < 0.01), streptococci (P < 0.001), Escherichia coli (P < 0.01), other members of the family Enterobacteriaceae (P < 0.02), and Pseudomonas aeruginosa (P < 0.05) was detected earlier in BacT/Alert aerobic bottles. Growth of S. aureus (P < 0.001), coagulase-negative staphylococci (P < 0.05), enterococci (P < 0.01), Streptococcus pneumoniae (P < 0.02), viridans group streptococci (P < 0.05), E. coli (P < 0.001), KlebsieUa pneumoniae (P < 0.01), and other members of the family Enterobacteriaceae (P < 0.001) was detected earlier in BacT/Alert anaerobic bottles. In a system-versus-system comparison, more grampositive cocci were recovered from the BACTEC system alone (P < 0.05), and more members of the family Enterobacteriaceae were recovered from the BacT/Alert system alone (P < 0.001). As a system, the BacT/Alert system detected growth of S. aureus (P < 0.001), coagulase-negative staphylococci (P < 0.01), streptococci (P < 0.001), E. coli (P < 0.001), other members of the family Enterobacteriaceae (P < 0.001), and P. aeruginosa (P < 0.05) earlier than the BACTEC system did. Significantly fewer (40 versus 1,183) false-positive results occurred with the BacT/Alert system. We conclude that the BacT/Alert and BACTEC 660/730 nonradiometric systems are comparable for recovering clinically significant microorganisms from adult patients with bacteremia or fungemia, but that the BacT/Alert system detects microbial growth earlier than the BACTEC system does, with significantly fewer false-positive results.

A new medium, FAN, designed to enhance the recovery of microorganisms, has been developed for the BacT/Alert blood culture system (Organon Teknika Corp., Durham, N.C.). We compared the yield and speed of detection of microorganisms in 6,847 adequately filled paired aerobic standard and FAN bottles at four university hospitals. Of 499 clinically significant microorganisms isolated from one or both bottles, significantly more Staphylococcus aureus isolates (P < 0.001), coagulase-negative staphylococci (P < 0.001), yeasts (P < 0.01), and all microorganisms combined (P < 0.001) were recovered from the FAN bottles. Overall, the speeds of detection of positive cultures did not differ between the two medium formulations; mean times to detection in the standard and FAN bottles were 16.1 and 16.0 h, respectively. When a subset of patients on antimicrobial therapy was evaluated, significantly enhanced yield from the FAN bottle was evident for staphylococci. Overall, the FAN bottle outperformed the standard aerobic BacT/Alert bottle.