What is the most common microbial agent transmitted by blood transfusion?

Most Common Microbial Agent Transmitted by Blood Transfusion

Cytomegalovirus (CMV) is the most common microbial agent transmitted through blood transfusion. While hepatitis viruses and HIV historically posed significant risks, modern screening has dramatically reduced their transmission rates, making CMV the most frequently transmitted agent today.

Evidence for CMV as Most Common Transmitted Agent

• CMV is highly prevalent in the general population, with 30-50% of adults showing serologic evidence of past infection 1
• CMV is transmitted primarily through cellular components of blood 2
• Unlike other viruses that have been virtually eliminated through screening, CMV remains a common transfusion-transmitted infection

Comparison of Transfusion-Transmitted Infections

Hepatitis C Virus (HCV)

• Historically was a major concern with transmission rates exceeding 20% in the 1960s 3
• Modern screening has reduced the risk to approximately 0.001% per unit transfused 3
• Implementation of nucleic acid testing (NAT) has virtually eliminated risks for HCV transmission 3

Hepatitis B Virus (HBV)

• Improved screening reduced post-transfusion hepatitis B rates from high levels to 0.3%-0.9% by mid-1970s 3
• Current incidence is estimated to be around 0.002% per transfusion recipient 3
• Remains a concern due to window period, immunovariant viruses, and occult HBV infection 4

HIV and Other Viruses

• Risk of HIV transmission has been drastically reduced through antibody screening 1
• Overall risk of transmission of HIV, HTLV, HBV, and HCV in the USA has been reduced to between one and four per million blood components transfused 5

Current Screening Practices

• Multiple overlapping safety measures are in place for hepatitis viruses and HIV:

  • Donor exclusion based on clinical history of risk factors
  • Serological marker screening
  • Nucleic acid testing (NAT)
  • Surrogate markers like ALT and anti-HBc testing 3, 6

• These measures have made transfusions safer than ever before 6

Clinical Implications

• CMV infection can cause severe primo-infections in immunodeficient individuals and pregnant women 1
• Patients with abnormal liver function tests after receiving blood products should be tested for hepatitis viruses 3
• Immunodeficient elderly and patients receiving immunosuppressive treatments may be susceptible to infection even with lower infectious doses 4

Common Pitfalls

• Relying solely on antibody testing can miss infections during the window period
• Failing to consider the recipient's immune status when investigating post-transfusion infections
• Overlooking the possibility of CMV transmission in immunocompromised patients

In conclusion, while hepatitis viruses and HIV were historically major concerns in blood transfusion, modern screening methods have dramatically reduced their transmission rates. CMV remains the most commonly transmitted microbial agent through blood transfusion due to its high prevalence in the general population and transmission through cellular blood components.