title: Asymptomatic Clostridium difficile colonization: epidemiology and clinical implications.
abstract: BACKGROUND
  The epidemiology of Clostridium difficile infection (CDI) has changed over the past decades with the emergence of highly virulent strains. The role of asymptomatic C. difficile colonization as part of the clinical spectrum of CDI is complex because many risk factors are common to both disease and asymptomatic states. In this article, we review the role of asymptomatic C. difficile colonization in the progression to symptomatic CDI, describe the epidemiology of asymptomatic C. difficile colonization, assess the effectiveness of screening and intensive infection control practices for patients at risk of asymptomatic C. difficile colonization, and discuss the implications for clinical practice.
  
  
  METHODS
  A narrative review was performed in PubMed for articles published from January 1980 to February 2015 using search terms 'Clostridium difficile' and 'colonization' or 'colonisation' or 'carriage'.
  
  
  RESULTS
  There is no clear definition for asymptomatic CDI and the terms carriage and colonization are often used interchangeably. The prevalence of asymptomatic C. difficile colonization varies depending on a number of host, pathogen, and environmental factors; current estimates of asymptomatic colonization may be underestimated as stool culture is not practical in a clinical setting.
  
  
  CONCLUSIONS
  Asymptomatic C. difficile colonization presents challenging concepts in the overall picture of this disease and its management. Individuals who are colonized by the organism may acquire protection from progression to disease, however they also have the potential to contribute to transmission in healthcare settings.
authors.affiliation: Research School of Population Health, The Australian National University, Building 62 Mills Road, Canberra, ACT 2601, Australia. luis.furuya-kanamori@anu.edu.au.
authors.forename: Luis
authors.initials: L
authors.lastname: Furuya-Kanamori
authors.affiliation: School of Population Health, The University of Queensland, Herston, QLD, Australia. john.marquess@health.qld.gov.au.|Queensland Department of Health, Communicable Diseases Unit, Herston, QLD, Australia. john.marquess@health.qld.gov.au.
authors.forename: John
authors.initials: J
authors.lastname: Marquess
authors.affiliation: Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK. laith.yakob@lshtm.ac.uk.
authors.forename: Laith
authors.initials: L
authors.lastname: Yakob
authors.affiliation: Microbiology and Immunology, School of Pathology and Laboratory Medicine, The University of Western Australia, Nedlands, WA, Australia. thomas.riley@uwa.edu.au.|PathWest Laboratory Medicine, Queen Elizabeth II Medical Centre, Nedlands, WA, Australia. thomas.riley@uwa.edu.au.
authors.forename: Thomas V
authors.initials: TV
authors.lastname: Riley
authors.affiliation: The University of Queensland, UQ Centre for Clinical Research, Herston, QLD, Australia. david.antibiotics@gmail.com.
authors.forename: David L
authors.initials: DL
authors.lastname: Paterson
authors.affiliation: PathWest Laboratory Medicine, Queen Elizabeth II Medical Centre, Nedlands, WA, Australia. niki.foster@health.wa.gov.au.
authors.forename: Niki F
authors.initials: NF
authors.lastname: Foster
authors.affiliation: The University of Queensland, UQ Centre for Clinical Research, Herston, QLD, Australia. c.huber@uq.edu.au.
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Huber
authors.affiliation: Research School of Population Health, The Australian National University, Building 62 Mills Road, Canberra, ACT 2601, Australia. director.rsph@anu.edu.au.
authors.forename: Archie C A
authors.initials: AC
authors.lastname: Clements
mesh_terms: D058345:Asymptomatic Infections; D001426:Bacterial Proteins / Q000378:metabolism; D001427:Bacterial Toxins / Q000378:metabolism; D016360:Clostridioides difficile / Q000472:pathogenicity*; D003015:Clostridium Infections / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission*; D004768:Enterotoxins / Q000378:metabolism; D054884:Host-Pathogen Interactions; D006801:Humans; D017053:Infection Control; D012307:Risk Factors; D013171:Spores, Bacterial
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004768:Enterotoxins; C041348:tcdA protein, Clostridium difficile; C031815:toxB protein, Clostridium difficile