The myth of occult hepatitis C infection
Authors: Philippe Halfon, Michele Martinot-Peignoux, Patrice Cacoub
Journal: Hepatology (2009)

We read with interest the review by Welker and Zeuzem on occult hepatitis C virus (HCV) infection and also the reply by Carreno et al.1, 2 The latter reported in their answer to Welker and Zeuzem that HCV can replicate in patients with occult HCV infection. Because this conclusion would have substantial consequences for patients considered cured of their HCV infection, as well as for the health care system, the data must be interpreted most carefully. They reported two studies that "unconvincingly failed to detect occult HCV infection in cryptogenic hepatitis because of several concerns with the methodology employed."3, 4 We would like to correct Carreno et al. on these two important points. In the first study published by Tanari et al., it was shown that the ability for HCV RNA detection is more sensitive in whole blood instead of peripheral blood mononuclear cells (PBMCs), due to circulation of the infectious virus in patient sera in the form of triglyceride-rich particles which is present in the whole blood and not in PBMCs.5 In the second study, we looked for the so-called "occult hepatitis C", in a different population of patients and controls, including patients with long-term normal alanine aminotransferase level, by using an original ultrasensitive validated real-time polymerase chain reaction (PCR) method. We failed to find any occult hepatitis C.4 Moreover, we would like to underscore that for a long time, Carreno et al. reported the same results on the same cohort of patients.6 The method proposed used PBMCs from a patient chronically infected with HCV for RNA isolation and HCV RNA detection. Serial dilutions of the isolated RNA cannot be a gold standard due to the limit of detection of HCV RNA by an in-house reverse transcription PCR method. PBMCs from our patients were subjected to HCV RNA transcription-mediated amplification assays without any HCV RNA detectable using this high sensitivity assay.6 The second issue addressed is related to the concept of the presence of HCV RNA in the liver in the absence of HCV RNA detected in PBMCs. Carreno et al. suggested that negativity for HCV-RNA in PBMC does not exclude the existence of occult HCV infection because the gold standard method to identify this occult infection is by detection of viral RNA in liver cells. To address this question, Maylin et al. recently assessed the presence of residual HCV RNA in serum, liver, and PBMCs using TMA (sensitivity <9.6 IU/mL) in a long-term follow-up study of patients infected with chronic hepatitis C who achieved a sustained virological response after interferon-based treatment.6 A total of 114 patients had a posttreatment liver tissue and 156 had PBMCs. Serum HCV RNA remained undetectable (1300 samples), indicating that none of the patients had a relapse. HCV RNA was detectable in 2 of 114 (1.7%) liver specimens, and in none of 156 PBMC specimens. These authors strongly suggest that SVR may be considered to show eradication of HCV infection.7 This latest observation was confirmed by another recent study with a complete clearance of HCV RNA from the PBMCs of blood donors who spontaneously or therapeutically control their plasma viremia.8 In conclusion, the excellent review performed by Welker and Zeuzem on occult HCV infection confirm our data and those of two other studies using sensitive assays and liver/PBMC assessment, and reinforce the absence of evidence of occult HCV infection. Philippe Halfon M.D., Ph.D.*, Michele Martinot-Peignoux Ph.D. , Patrice Cacoub M.D., Ph.D. , * Département Virologie Laboratoire Alphabio, Service Maladie Infectieuses Hôpital Ambroise Paré, Marseille, France, Université Paris VII, Hôpital Beaujon, Clichy, France; Service de Microbiologie, Hôpital Beaujon, Clichy, France; Institut National de la Santé et de la Recherche Médicale U-773, Centre de Recherche Biomédicale Bichat-Beaujon CRB3, Hôpital Beaujon, Clichy, France, Université Pierre et Marie Curie-Paris 6, Centre National de la Recherche Scientifique, UMR 7087, Paris, France; Hôpital Pitié-Salpêtrière, Service de Médecine Interne, Assistance Publique–Hôpitaux de Paris, Paris, France.