Hepatitis C virus infection in blood donors from Castilla y Leon, Spain. Eva López García, Complejo Asistencial de Salamanca, Spain. Servicio de Medicina Preventiva y Salud Pública. 14 July 2010 To The Editor: In the January 25th issue of Virology Journal, Sosa-Jurado and colleagues analyzed the prevalence of antibodies to hepatitis C virus (HCV) in blood donors from Puebla, Mexico. The prevalence found in this study (0.84%; 515/61553)  is situated in an intermediate position in respect to the other series that have been studied in other countries like Germany (0.29%; 3/1020) , Australia (0.55%; 190/34725) , India (0.61%; 37/6109) , Brazil (1.15%; 298/25891) , Indonesia (2.13%; 161/7572) , Iran (2.32%; 55/2376) , Niger (2.9%; 29/1000)  or Georgia (7.8%; 43/553) . In Spain, the prevalence of infection for HCV has been an objective of small studies that were carried out in general population [10,11], as well as in specific groups like pregnant women , parental drugs users  or prisoners . Nevertheless, HCV antibodies frequency in donors blood has been scantily studied because no updated information is available [15,16]; for this reason, this investigation was carried on. We conducted a cross-sectional descriptive study on sample which was obtained by consecutive sampling of all first-time blood donors from the Center of Hemotherapy and Hemodonation of Castilla y Leon (Spain), in the period between 1 January 2004 and 31 December 2007. To be eligible as a donor, it is required to be between 18-60 years old, in general good health condition and successfully undergo a screening process that includes the completion of a questionnaire and interview process by trained health professionals. Variables in the questionnaire were having had previous blood transmitted infections, having received an organ transplant, having taken money or drugs for sex, or having had a sexual partner that has participated in the last two high risk activities. Other variables were having had dental work, major surgery or endoscope, acupuncture, tattoos or body piercing in the last four months and having received transfusion or live with hepatitis carrier status person in the past four months. Serum blood donations were screened for the detection of qualitative antibodies to HCV using the Abbott PRISM HCV chemiluminescent immunoassay in vitro (ChLIA). The above mentioned system possesses antigens recombinants c100-3, HCr43 and NS5, that detect the antigens of the core (NS3, NS4, NS5). 49 HCV antibody-positive donations were identified from 85263 donations in the 3-year period, January 2004 to December 2007, which gives a prevalence of 0.05%. Our investigation constitutes the major worldwide series documented up to now, conducted on blood donors in whom the presence of antibodies to HCV had been studied. The prevalence results obtained are far lower than the ones found by Sosa-Jurado in Mexico . A key element can explain these different figures; the fact that every person, in our country, who wants to donate blood is submitted to a screening questionnaire in order to defer the ineligible donors. Nevertheless, the Sosa-Jurado study  does not specify if such an important component in the process of donation (as the accomplishment of the above mentioned questionnaire), had been carried out. In the same way, there is a lack of detailed description of the variables that would come through the mentioned questionnaire. The non inclusion of this information limits the validity of the results obtained by Sosa-Jurado on the real prevalence of antibodies to HCV in blood donors. It also nullifies out any possible comparisons with other works like ours, since, if initially this questionnaire was not realized strictly with persons that were about to donate (and not only to the donors who presented HCV antibodies, since it seems like this is what had been done by Sosa-Jurado) there would be a classification bias that would lead to an overestimated prevalence. Further on, not knowing the variables of the questionnaire does not allow us to do valid comparisons, because it is known that the stricter the questionnaire requirements are, the lowest HCV frequency will be found. For all these reasons, we think that those aspects must be specified in any future study that will be realized on this topic. References  Sosa-Jurado F, Santos-López G, Guzmán-Flores B, Ruiz-Conde JI, Meléndez-Mena D, Vargas-Maldonado MT, Martínez-Laguna Y, Contreras-Mioni L, Vallejo-Ruiz V, Reyes-Leyva J: Hepatitis C virus infection in blood donors from the state of Puebla, Mexico. 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Centro de Hemoterapia y Hemodonación de Castilla y León, Valladolid. Spain. Competing interests The authors declare that they have no competing interests.