What is the most common virus transmitted by blood transfusion?

The Most Common Virus Transmitted by Blood Transfusion

Hepatitis C virus (HCV) is the most common virus transmitted by blood transfusion. While modern screening has dramatically reduced transmission rates, historically HCV has been the predominant transfusion-transmitted viral infection 1.

Historical Context and Epidemiology

Hepatitis C virus was identified in 1988 as the primary cause of what was previously known as "non-A, non-B hepatitis." Before the implementation of donor screening:

• In the 1960s, post-transfusion hepatitis rates exceeded 20% 1
• By the late 1970s, prospective studies showed approximately 10% of transfusion recipients developed non-A, non-B hepatitis (later identified as primarily HCV) 1
• Studies demonstrated that 90% of post-transfusion hepatitis was not caused by hepatitis A or B viruses 1

Relative Risk Comparison

When comparing the major transfusion-transmitted viruses:

• Hepatitis C (HCV): Historically the most common transfusion-transmitted virus, accounting for the majority of post-transfusion hepatitis cases 1
• Hepatitis B (HBV): By the mid-1970s, improved screening reduced transfusion-related HBV infection rates to 0.3%-0.9% per transfusion recipient 1
• HIV: While significant, HIV has never been the most common transfusion-transmitted virus 2
• CMV: Primarily transmitted through cellular components rather than plasma, affecting mainly immunocompromised recipients 3

Current Risk Status

Modern blood screening has dramatically reduced transmission risks:

• Current risk of transfusion-transmitted HCV is estimated at 1 in 125,000 units 4
• HBV transmission risk is approximately 1 in 63,000 units 4
• Overall viral transmission risk in the USA has been reduced to between one and four per million blood components transfused 5

Screening Evolution

The dramatic reduction in transmission rates resulted from:

• Shift from paid to volunteer blood donors 1
• Implementation of anti-HCV antibody screening
• Addition of nucleic acid testing (NAT) for HCV
• Implementation of surrogate markers like ALT and anti-HBc testing 1

Key Points for Clinical Practice

• Despite advanced screening, zero risk has not been achieved for any transfusion-transmitted virus 2
• Patients with abnormal liver function tests after receiving blood products should be tested for HCV and other hepatitis viruses 1
• The European Association for the Study of the Liver (EASL) recommends that blood donor services screen blood donors for hepatitis viruses by NAT, informed by local risk assessment 1

Common Pitfalls

• Assuming modern blood supply is completely safe; while risks are extremely low, they are not zero
• Failing to consider transfusion-transmitted viral infection in patients with unexplained hepatitis following transfusion
• Overlooking that immunocompromised recipients may be more susceptible to infection even with lower viral loads 6

While current screening has dramatically reduced transmission risks, hepatitis C virus remains historically the most common virus transmitted through blood transfusion, with hepatitis B virus being the second most common.