title: Occult HCV Infection: The Current State of Knowledge.
abstract: BACKGROUND
  Occult HCV infection (OCI) is defined as the presence of HCV-RNA in hepatocytes and the absence of HCV in the serum according to usual tests. We aimed to define OCI and provide information about the currently available diagnostic methods. Then we focus on specific groups that are at high risk of OCI and finally investigate immune responses to OCI and the available treatment approaches.
  
  
  METHODS
  PubMed, Scopus and Google Scholar were comprehensively searched with combination of following keywords: "occult", "hepatitis C virus" and "occult HCV infection". The definition of OCI, diagnostic methods, specific groups that are at high risk and available treatment approaches were extract from literature. An analysis of available articles on OCI also was done based on Scopus search results.
  
  
  RESULTS
  OCI has been reported in several high-risk groups, especially in hemodialysis patients and subjects with cryptogenic liver disease. Furthermore, some studies have proposed a specific immune response for OCI in comparison with chronic hepatitis C (CHC).
  
  
  CONCLUSIONS
  With a clinical history of approximately 11 years, occult HCV infection can be considered an occult type of CHC. Evidences suggest that considering OCI in these high-risk groups seems to be necessary. We suggest that alternative diagnostic tests should be applied and that there is a need for the participation of all countries to determine the epidemiology of this type of HCV infection. Additionally, evaluating OCI in blood transfusion centers and in patients who receive large amounts of blood and clotting factors, such as patients with hemophilia, should be performed in future projects.
authors.affiliation: Students' Research Committee, Baqiyatallah University of Medical Sciences, Tehran, IR Iran; Middle East Liver Diseases Center (MELD), Tehran, IR Iran.
authors.forename: Mohammad Saeid
authors.initials: MS
authors.lastname: Rezaee-Zavareh
authors.affiliation: Middle East Liver Diseases Center (MELD), Tehran, IR Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Hadi
authors.affiliation: Students' Research Committee, Baqiyatallah University of Medical Sciences, Tehran, IR Iran.
authors.forename: Hamidreza
authors.initials: H
authors.lastname: Karimi-Sari
authors.affiliation: Students' Research Committee, Baqiyatallah University of Medical Sciences, Tehran, IR Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hossein Khosravi
authors.affiliation: Students' Research Committee, Baqiyatallah University of Medical Sciences, Tehran, IR Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Ajudani
authors.affiliation: Students' Research Committee, Baqiyatallah University of Medical Sciences, Tehran, IR Iran.
authors.forename: Fardin
authors.initials: F
authors.lastname: Dolatimehr
authors.affiliation: Students' Research Committee, Baqiyatallah University of Medical Sciences, Tehran, IR Iran.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Ramezani-Binabaj
authors.affiliation: Middle East Liver Diseases Center (MELD), Tehran, IR Iran; Kowsar Medical Institute, Heerlen, The Netherlands.
authors.forename: Seyyed Mohammad
authors.initials: SM
authors.lastname: Miri
authors.affiliation: Middle East Liver Diseases Center (MELD), Tehran, IR Iran; Baqiyatallah Research Center for Gasteroenterology and Liver Disease (BRCGL), Baqiyatallah University of Medical Sciences, Tehran, IR Iran.
authors.forename: Seyed Moayed
authors.initials: SM
authors.lastname: Alavian
keywords: Hepatitis C; Knowledge; Occult infection; Review