Michael Towns

Guidelines on Blood Cultures

Just over one-third of sepsis patients have positive blood cultures, mainly due to inadequate sampling volumes (50% of adults have < 1.0 CFU/mL blood) and the prior use of antibiotics. However, 20-30% of sepsis patients are given inappropriate empirical antibiotics. The Clinical and Laboratory Standards Institute guidelines recommend paired culture sets to help discriminate between contaminant organisms and true pathogens; four 10-mL bottles (2 sets) should be used for the initial evaluation to detect about 90-95% of bacteremias and six 10-mL bottles (3 sets) should be used to detect about 95-99% of bacteremias. It has also been shown that the positivity rate increased by 15-35% with resin-based media in patients on antibiotics. For diagnosing catheter-related bloodstream infections, differential time-to-positivity is one method recommended to help determine whether the catheter is truly the source of infection. The proper training of personnel with regard to drawing an appropriate blood volume and the importance of clear labeling of culture bottles is also of critical importance. Furthermore, if the contamination rate is relatively high, hiring dedicated staff who are well-trained in order to get a lower blood culture contamination rate may be cost-effective. It is because high false-positive blood culture rates due to contamination are associated with significantly increased hospital and laboratory charges.

Clostridium difficile: Colonization and Toxin Production in a Cohort of Patients With Malignant Hematologic Disorders

We examined 45 (80%) of 56 consecutive adult patients with malignant hematologic disorders who were hospitalized during a 15-week period at Emory University Hospital, Atlanta. Stool samples for Clostridium difficile culture and cytotoxin assay were obtained on admission and then weekly during each patients hospitalization. On admission, four patients had detectable C difficile in their stool samples, which was associated with prior antimicrobial use but not with prior cancer chemotherapy. One of the four patients with positive stool samples also had toxin present in the stool sample and was the only one with diarrhea. Eight (36%) of 22 patients hospitalized for one or more weeks had C difficile isolated from at least one stool specimen. The positive cultures showed no clustering in time, and no risk factors were identified for colonization. Only seven of 15 culture-positive stool samples and three of seven toxin-positive samples were associated with diarrhea.

Differential expression of toll-like receptor genes: sepsis compared with sterile inflammation 1 day before sepsis diagnosis.

Toll-like receptors (TLRs) are critical components of innate immunity. This study was designed to evaluate differential expression of genes for TLR and associated signal transduction molecules in critically ill patients developing sepsis compared with those with sterile inflammation. Uninfected critically ill patients with systemic inflammatory response syndrome were prospectively followed daily for development of sepsis. They were divided into two groups and compared in a case-control manner: (a) preseptic patients (n = 45) who subsequently developed sepsis, and (b) uninfected systemic inflammatory response syndrome patients (n = 45) who remained uninfected. Whole blood RNA was collected (PAXGene tube) at study entry and 1, 2, and 3 days before clinical sepsis diagnosis (or time-matched uninfected control) and analyzed via Affymetrix Hg_U133 Plus 2.0 microarrays. Genes were considered differentially expressed if they met univariate significance controlled for multiple comparisons at P < 0.005. Differentially expressed probes were uploaded into the Database for Annotation, Visualization and Integrated Discovery. The TLR pathway (Kyoto Encyclopedia of Genes and Genomes-KEGG) significance was determined via Expression Analysis Systematic Explorer (EASE) scoring. A total of 2,974 Affymetrix probes representing 2,190 unique genes were differentially expressed 1 day before sepsis diagnosis. Thirty-six probes representing 25 genes were annotated to the TLR pathway (KEGG) via the Database for Annotation, Visualization and Integrated Discovery with an EASE score at P < 0.0004. Notable TLR genes demonstrating increased expression include TLR-4 (median, 1.43-fold change), TLR-5 (2.08-fold change), and MAPK14 (1.90-fold change). An additional 11 unique genes were manually annotated into the TLR pathway based on known relevance such as TLR-8 (1.54-fold change). The total 36 genes contained 28 showing increased expression and 8 showing decreased expression. Differential gene expression was noted for TLR receptors (eight genes), TLR intracellular signal transduction cascade molecules (27 genes), and TLR-related effector molecules (one gene). The TLR and downstream signaling genes are differentially expressed in critically ill patients developing sepsis compared with those with sterile inflammation. These expression differences occur before phenotypic-based diagnosis of clinical sepsis.