This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hepatitis, Subject name: Medicine
Why pre-transfusion testing does not decrease the incidence of hepatitis? 
Select and explain. 
A. Most carriers do not have HBsAg, B. Post transfusions hepatitis is caused by CMV, C. Present screening test is not sensitive for HBsAg, D. HCV not screened
B: Post transfusions hepatitis is caused by CMV
Answer: B: Post transfusions hepatitis is caused by CMV 
Explanation: Possible reasons for post transfusion hepatitis by CMV in spite of screening: CMV persists in blood monocytes and 50-60% of adults are lifelong carriers of the virus. Hence it can be transmitted by transfusion of cellular blood components. Transfusion transmitted CMV can cause problems in premature neonates, allograft recipients, splenectomized patients. Problem with Hepatitis B testing and our strategy to bypass it HBsAg is not detected during the window period between disappearance of HBsAg and appearances of IgM Ab HBs. Anti HBc IgM is detected in this window period which is hence used in screening methods.