Bloodstream Infections

The spectrum of microorganisms causing bacteremia and fungemia in immunocompromised hosts has changed over the last decade, owing in large part to widespread use of chemoprophylaxis, differences in immunosuppressive regimens, and significant increases in the use of long-term indwelling devices. This chapter discusses the approach to immunocompromised patients with suspected bacteremia and fungemia, with particular emphasis on culture-independent diagnostic methods. The authors briefly address the predilection of specific microorganisms to cause invasive bloodstream infections among certain immunocompromised populations and discuss individual risk factors associated with the development of bacteremia and fungemia. The culturing of blood from patients with suspected bloodstream infections has remained one of the most important diagnostic tests performed by the microbiology laboratory. Over the last several decades, improvements in blood culture media and continuously monitoring blood culture systems have greatly enhanced the diagnostic value of blood cultures for the detection of bacteremia and candidemia. The sensitivity of blood cultures is excellent for the detection of nonfastidious bacterial pathogens and increases with the volume of blood collected. Laboratorians can continue to optimize the use of blood cultures for the diagnosis of bloodstream infections and to encourage their clinicians to obtain at least two sets of blood cultures by separate venipuncture before starting antimicrobial therapy.