Highlights•Occult hepatitis C infection (OCI) identified in injection drug users (IDUs) with direct-acting antivirals (DAAs) therapy and HCV spontaneous resolution) by droplet digital PCR (ddPCR).•OCI IDUs with DAAs therapy might not be entirely cured.•OCI IDUs without DAAs therapy identified due to tested PBMCs samples.•Hight percentage of HCV-RNA detected in red blood cells (RBCs).•HCV/OCI identification with PBMCs and RBCs samples as a predictor.