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.

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.

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia but is undoubtedly underdiagnosed. Isolation of S. pneumoniae from blood is specific but lacks sensitivity, while isolation of S. pneumoniae from sputum may represent colonization. We evaluated a new immunochromatographic test (NOW S. pneumoniae urinary antigen test; Binax, Portland, Maine) that is simple to perform and that can detect S. pneumoniae antigen in urine within 15 min. Urine samples from 420 adults with community-acquired pneumonia and 169 control patients who did not have pneumonia were tested. Urine from 315 (75%) of the pneumonia patients and all controls was tested both before and after 25-fold concentration, while the remaining 105 samples were only tested without concentration. S. pneumoniae urinary antigen tests were positive for 120 (29%) patients with pneumonia and for none of the controls. Of the urine samples tested with and without concentration, 96 were positive, of which 6 were positive only after concentration. S. pneumoniae antigen was detected in the urine from 16 of the 20 (80%) patients with blood cultures positive for S. pneumoniae and from 28 of the 54 (52%) patients with sputum cultures positive for S. pneumoniae. The absence of S. pneumoniae antigen in the urine from controls suggests that the specificity is high. Concentration of urine prior to testing resulted in a small increase in yield. The NOW S. pneumoniae urinary antigen test should be a useful adjunct to culture for determining the etiology of community-acquired pneumonia in adults.Streptococcus pneumoniae has consistently been shown to be the most common cause of community-acquired pneumonia (CAP) in both adults and children. S. pneumoniae accounts for about two-thirds of cases where an etiologic diagnosis is made (12) and is likely to be the leading cause of pneumonia of otherwise unknown etiology (19). Despite being the single most important pathogen causing CAP, S. pneumoniae is undoubtedly underdiagnosed due to limitations of conventional diagnostic tests. Isolation of S. pneumoniae from blood lacks sensitivity, isolation of S. pneumoniae from sputum may represent colonization, and lung aspirates are rarely performed. In an effort to improve the diagnostic yield for patients with suspected pneumonia, there has been a considerable interest in alternative techniques, such as PCR and antigen detection.Detection of S. pneumoniae antigens in the urine of patients with pneumonia was first described in 1917 (8). Over the intervening years the detection of S. pneumoniae antigens (usually capsular polysaccharides) in urine has been extensively studied using a variety of techniques, including counterimmunoelectrophoresis, latex agglutination, coagglutination, and enzyme-linked immunosorbent assay (1, 2, 5, 6, 14, 23). To date, the performance of these tests has been variable, such that they have never received general acceptance.Recently, an immunochromatographic test, the NOW S.pneumoniae urinary antigen test (Binax, Inc., Portland, Maine), h...