title: Estimating risk of C. difficile transmission from PCR positive but cytotoxin negative cases.
abstract: BACKGROUND
  The use of molecular methods to diagnose Clostridium difficile infection (CDI) has improved diagnostic yield compared to conventional methods. However, PCR testing can detect colonization and has introduced several practical challenges pertaining to need for treatment and isolation of cases.
  
  
  METHODS
  For all new cases detected by real-time PCR, concurrent cytotoxin assay was performed and genetic characterization with MLVA (multi-locus variable number tandem repeat analysis) was done to determine relatedness. We used PCR cycle threshold (Ct) of detection as surrogate marker for bacterial burden in stool.
  
  
  RESULTS
  Overall, 54 cases of CDI were detected during the study period. 42 were concurrently tested by CYT and characterized by MLVA .MLVA analysis revealed marked genetic diversity with no ongoing outbreaks; four cases were due to NAP1 strain. CYT -/PCR + cases had a higher median Ct value of detection compared to CYT+/PCR + cases (28.2 vs 22.5; p = 0.01). Among 25 strains that were genetically related, 9/11 isolates in this dominant cluster were positive by CYT compared to 4/14 in non-dominant clusters (p = 0.02).
  
  
  CONCLUSIONS
  CYT-/PCR+ cases contribute to hospital based transmission. However, the risk of transmission of C. difficile from CYT +/PCR+ cases may be higher than those that are CYT-/PCR+.
authors: Infection Control Program, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America ; Infectious Diseases Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: Mini
authors: M
authors: Kamboj
authors: Clinical Microbiology Service, Department of Laboratory Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: N Esther
authors: NE
authors: Babady
authors: Division of Infectious Diseases, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors: Jane W
authors: JW
authors: Marsh
authors: Division of Infectious Diseases, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors: Jessica L
authors: JL
authors: Schlackman
authors: Infection Control Program, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: Crystal
authors: C
authors: Son
authors: Infectious Diseases Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: Janet
authors: J
authors: Sun
authors: Infection Control Program, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: Janet
authors: J
authors: Eagan
authors: Infectious Diseases Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America ; Clinical Microbiology Service, Department of Laboratory Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: Yi-Wei
authors: YW
authors: Tang
authors: Infection Control Program, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America ; Infectious Diseases Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: Kent
authors: K
authors: Sepkowitz
mesh_terms: D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D016360:Clostridioides difficile / Q000235:genetics; D003015:Clostridium Infections / Q000175:diagnosis / Q000382:microbiology* / Q000635:transmission*; D016000:Cluster Analysis; D003603:Cytotoxins / Q000737:chemistry*; D004196:Disease Outbreaks; D005260:Female; D005838:Genotype; D006801:Humans; D007124:Immunoenzyme Techniques; D007223:Infant; D007297:Inpatients; D008297:Male; D016133:Polymerase Chain Reaction; D012306:Risk; D020080:Tandem Repeat Sequences / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D003603:Cytotoxins