The most recent review of nosocomial bloodstream infections, released by the National Healthcare Safety Network (NHSN) in 2007 ( 10) estimates that the rate of infection of central lines ranges from 1.5 to 6.8 per 1,000 central line days. Catheter-related infections account for an estimated 11-37% ( 1) of nosocomial bacteremias. While the prevalence of central lines has decreased, the use of peripherally-inserted central catheters (PICC) has increased significantly. Some have suggested that at least as many as four sets of blood cultures may be needed to achieve better detection rates ( 16). Given the increasing use of empiric antibiotics, the sensitivity of the 2 blood cultures specimen is not always optimal. At least 10-15 minutes should elapse between collection of the first and second blood specimen. In spite of the fact that the sensitivity of the blood cultures increases proportionally to the amount of blood drawn, the current automated systems provide an adequate accuracy with 8-10 cc of blood volume ( 4). Except for pediatric blood cultures, at least 2 bottles with 8-10cc of blood per bottle are required for proper specimen processing. The culture bottle should be cleansed with 70% alcohol and blood injected without needle change. Care should be taken not to contaminate the venipuncture site after preparation and prior to phlebotomy. The proper technique for obtaining blood cultures requires thorough cleaning of the skin surface with 70% alcohol followed by iodine-based preparation or 0.5 % chlorhexidine for 1-2 minutes ( 19, 23). This chapter attempts to provide general recommendations for such a clinical situation. However, no guidelines exist regarding the initial selection of antibiotics based on the preliminary results of the Gram stain. The Infectious Diseases Society of America (IDSA) and other organizations have issued recommendations for the treatment of bacteremia in the context of catheter-related infections that include both empirical and specific organism-based treatment protocols. Until molecular techniques for detection of bacteria in blood cultures are more readily available and easier to implement ( 25, 31), clinicians will have to continue to rely on the Gram stain as the preliminary source of data for making empiric therapeutic decisions. The field of PCR-based detection of organism is rapidly becoming a helpful tool in the identification and diagnosis of blood-stream infections, especially those caused by Gram-positive cocci ( 25, 28, 33). Once an organism has been fully identified, the antibiotic selection can be modified. Because of the high morbidity and mortality associated with bacteremia, prompt evaluation and appropriate empiric antibiotic treatment are of paramount importance ( 3). While patients with positive blood cultures may be bacteremic signifying a true infection, there is a subset of patients with positive blood cultures that are due to contamination and therefore does not indicate a true infection. Bacteria are only partially identified on Gram stain and speciation and susceptibility results will take an additional 24-48 hours after a culture is reported as positive. The appropriate selection of e mpiric antibiotic therapy for positive blood cultures is a complex and difficult decision.
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