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.

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The critical role of the microbiology laboratory in infectious disease diagnosis calls for a close, positive working relationship between the physician and the microbiologists who provide enormous value to the health care team. This document, developed by both laboratory and clinical experts, provides information on which tests are valuable and in which contexts, and on tests that add little or no value for diagnostic decisions. Sections are divided into anatomic systems, including Bloodstream Infections and Infections of the Cardiovascular System, Central Nervous System Infections, Ocular Infections, Soft Tissue Infections of the Head and Neck, Upper Respiratory Infections, Lower Respiratory Tract infections, Infections of the Gastrointestinal Tract, Intraabdominal Infections, Bone and Joint Infections, Urinary Tract Infections, Genital Infections, and Skin and Soft Tissue Infections; or into etiologic agent groups, including Tickborne Infections, Viral Syndromes, and Blood and Tissue Parasite Infections. Each section contains introductory concepts, a summary of key points, and detailed tables that list suspected agents; the most reliable tests to order; the samples (and volumes) to collect in order of preference; specimen transport devices, procedures, times, and temperatures; and detailed notes on specific issues regarding the test methods, such as when tests are likely to require a specialized laboratory or have prolonged turnaround times. There is redundancy among the tables and sections, as many agents and assay choices overlap. The document is intended to serve as a reference to guide physicians in choosing tests that will aid them to diagnose infectious diseases in their patients.

A blood culture is defined as a specimen of blood obtained from a single venipuncture or intravenous access device. There have been numerous changes in blood culture media and systems during the past 30 years (1,3,5,6,8). Newer media reportedly are more sensitive for the detection of microorganisms, and modern, automated, continuous-monitoring blood culture systems (CMBCSs) detect positive results 1 to 1.5 days earlier than previously used conventional blood culture systems (2, 4).Studies reported in the 1970s, 1980s, and early 1990s suggested that two to three blood cultures from adults obtained during a 24-h period could detect Ͼ99% of all bloodstream infections (BSIs) (1,5,7,8). However, a 2004 study from the Mayo Clinic using the BACTEC 9240 CMBCS found that two blood cultures detected only 80% of BSIs, that three detected 96% of BSIs, and that four were required to detect 100% of BSIs (3). This observation was unexpected given the use of a modern CMBCS and contemporary culture media. The authors hypothesized that newer systems may detect bacteremia at lower levels than older systems do and that more blood cultures are necessary to detect low-level bacteremia. To determine whether the observations were unique to the Mayo Clinic and its patient population, we systematically reviewed blood cultures at two geographically unrelated university medical centers to determine the cumulative sensitivity of blood cultures obtained sequentially during a 24-h period. MATERIALS AND METHODSAll positive blood cultures from adult inpatients at Robert Wood Johnson University Hospital, New Brunswick, NJ, and Duke University Medical Center, Durham, NC, from 1 January 2004 through 31 December 2005 were evaluated for inclusion in the study. At Robert Wood Johnson University Hospital, the BACTEC 9240 blood culture system with aerobic resin and anaerobic lytic blood culture medium was used. At Duke University Medical Center, the BACTEC 9240 blood culture system with the same medium or the BACT/ALERT blood culture system with activated charcoal medium, FA and FN, was used. A blood culture consisted of 20 ml of blood obtained either by venipuncture or from an intravenous access device. All instances in which Ն3 blood cultures per patient were obtained during a 24-h period were included. The medical records of patients who met the inclusion criteria were reviewed by one of the investigators to determine the clinical significance (true infection versus contamination) of the positive blood culture. Only patients whose positive blood cultures were judged to represent true infection were included.

The critical nature of the microbiology laboratory in infectious disease diagnosis calls for a close, positive working relationship between the physician/advanced practice provider and the microbiologists who provide enormous value to the healthcare team. This document, developed by experts in laboratory and adult and pediatric clinical medicine, provides information on which tests are valuable and in which contexts, and on tests that add little or no value for diagnostic decisions. This document presents a system-based approach rather than specimen-based approach, and includes bloodstream and cardiovascular system infections, central nervous system infections, ocular infections, soft tissue infections of the head and neck, upper and lower respiratory infections, infections of the gastrointestinal tract, intra-abdominal infections, bone and joint infections, urinary tract infections, genital infections, and other skin and soft tissue infections; or into etiologic agent groups, including arthropod-borne infections, viral syndromes, and blood and tissue parasite infections. Each section contains introductory concepts, a summary of key points, and detailed tables that list suspected agents; the most reliable tests to order; the samples (and volumes) to collect in order of preference; specimen transport devices, procedures, times, and temperatures; and detailed notes on specific issues regarding the test methods, such as when tests are likely to require a specialized laboratory or have prolonged turnaround times. In addition, the pediatric needs of specimen management are also emphasized. There is intentional redundancy among the tables and sections, as many agents and assay choices overlap. The document is intended to serve as a guidance for physicians in choosing tests that will aid them to quickly and accurately diagnose infectious diseases in their patients.