Knowing which subtype of Hepatitis C virus causes hepatitis is a determining factor when choosing the treatmentAlmost 1,500 Hospital patients participated in the studyThe subtype of virus is determined thanks to the high resolution mass sequencing The research group in  Liver Diseases of Vall d'Hebron Research Institute has recently published in the Clinical Microbiology and Infection journal a study on the determination of the type of virus that infects patients of Hepatitits C (HCV). The trial, led by Drs. Josep Quer and Francisco Rodríguez-Frías, has detected up to 22 different subtypes out of the 67 possible ones in the population of patients with chronic HCV infection.The study was conducted with patients who came to the Hospital with chronic infection by HCV, and that had not been treated yet or that the treatment had not worked. In total, 1.473 patients participated. Samples were taken from them and the type of hepatitis C virus with which they were infected was characterized. The characterization was carried out with next-generation sequencing techniques, that is to say, determining the sequence of the DNA of thousands of viruses that are circulating in the blood of these patients, in order to be able to distinguish them.They identify up to 22 different subtypes of Hepatitis C virus. Half of the patients were infected by subtype 1b and almost one-third with the subtype 1a. Surprisingly, 1 out of every 100 patients were infected by two or more subtypes at the same time. The study found that the majority of patients with chronic HCV infection were born before 1976 and, conversely were very few born after 1989, which is when it was discovered the virus.The results of this study are of great importance when it comes to choose the treatment that is given to each patient. Those affected by HCV are treated with Direct Action Antivirals (DAAs), which are small molecules that inhibit directly the life cycle of the virus. The patient's response to this treatment may vary depending on the type of virus that affects them. Therefore, the use of a method of subtyping without errors, like in this study, allows to make the best therapeutic decision and that the patient has the highest probability of eliminating the virus with the first treatment, thus preventing the resistance. Hepatitis C in Vall d'HebronAlthough the efficacy of the treatment of HCV is very high, the use of low resolution subtyping methods make some mistakes that sometimes make the first treatment that is administered to the patient not work. The method presented in this article, does not make mistakes identifying the subtype of VHC, causing the mean of recoveries to reach a 98.5% with the first treatment at the Hospital Vall d'Hebron. It is crucial to know the subtype of Hepatitis C virus in order to make the best choice of treatment, which prevents selected mutations of resistance and avoid large costs of medication.