Transfusion-Transmissible Diseases

Description

Infectious diseases may be transmitted in spite of careful selection of donors and testing of blood. Donor selection criteria are designed to screen out individuals who are at an increased risk for HIV, HTLV, and hepatitis infection. For each donation, a donor sample is tested for:

• antibodies to Human Immunodeficiency Virus (HIV-1 and HIV-2), Human T-cell Lymphotropic Virus (HTLV-I/II), Hepatitis C Virus (HCV), HB core antigen
• the presence of Hepatitis B Surface antigen (HBsAg),
• Syphilis and
• the presence of viral RNA (HIV-1, HCV and WNV)

Note: All donor testing is performed using methods and reagents authorized by Health Canada.

Only units found negative on approved tests for these transmissible disease markers are released. However, these tests do not totally eliminate the risk of transmitting the corresponding infectious agent. Alternatives to blood and blood products should be considered, where feasible.

Cytomegalovirus (CMV) may be of concern for certain patients. To reduce the frequency of CMV transmission, Canadian Blood Services manufactures leukoreduced cellular components. For some patients at particularly high risk of severe CMV disease, (e.g., fetus requiring Intra Uterine Transfusion *IUT), or a CMV-seronegative, allogenic, hematopoietic stem cell recipient), clinicians may choose, in addition to the use of LR components, to transfuse components from CMV-seronegative donors.

Trypanosoma Cruzi (T. Cruzi) or Chagas, is a disease widely endemic in South America. There have been documented cases of transfusion-transmitted Chagas in North America, including Canada. For this reason Canadian Blood Services has implemented additional screening questions for donors. Any donor who answers ‘yes’ to a Chagas risk question has their blood tested for the presence of T. Cruzi antibodies.

In life-threatening situations, the administration of leukoreduced blood and blood components should not be delayed due to unavailability of CMV-seronegative blood.

Other infectious agents, rarely transmitted by blood include babesia, bartonella, borrelia, brucella, the agent of Colorado tick fever, leishmania, parvovirus, plasmodia, toxoplasma and certain other typanosomes. While all potential blood donors are subjected to stringent screening procedures intended to reduce to a minimum the risk that they will transmit infectious agents, there are no routinely available tests to predict or prevent transmission of these infectious agents.

Recent studies suggest that variant Creutzfeldt-Jakob Disease (vCJD) may be transmitted by blood transfusion. Although donors are questioned with respect to risk factors for developing vCJD, and are deferred from donations if such risk factors exist, there is no screening test for this illness.

Incidence

Because rates are so low in Canada and other developed countries, it is extremely difficult to measure these risks with accuracy. Estimations are further complicated because symptoms may not appear for many years and are difficult to link to prior transfusion. 

See Table 1 for a summary of current estimated risks in Canada. The estimated risks are for infection, not clinically significant disease, whose rates may be lower.

Table 1. Risk of transfusion-transmitted infection in Canada*

	Residual Risk per RBC or Platelet Unit Kleinman, S. et al	Residual Risk per 1,000,000 donations (95% CI)*** Chiavetta, J. et al
HIV	1/4,700,000	0.24 (0.03-0.62)+
HCV	1/3,100,000	0.70 (0.08-3.13)
HBV	1/31,000 to 1/82,000 *	8.52 (4.44-15.11)++
HTLV I/II	1/1,900,000 **	0.67 (0.24-1.42)

*In the presence of anti-HBcore testing the correct estimate may be closer to 1/82,000, however in the absence of anti-HBcore testing (as is the case for CBS donations), the figure is likely closer to 1/31,000.
**Figure based on USA data as no Canadian data exits. The incidence in Canada is likely to be lower given the lower donor prevalence rates (12 per 100,000 first time Canadian donors vs 35 per 100,000 first time USA donors).
*** On average each whole blood donation is used to prepare approximately 1.5 transfusable blood components.
+ Estimations performed using data collected during HIV p24 Antigen testing but prior to HIV RNA testing. The introduction of HIV RNA testing is estimated to have reduced the residual risk of HIV transmission by approximately 31.2% (Chiavetta J et al).
++ This risk assessment was performed using methods that had been previously used in the USA; however anti-HBcore testing is performed in the USA, but is not performed on CBS donations.

Others

• malaria -1 in 4 million red cells transfused
• syphilis -virtually zero
• Trypanosome cruzi (Chagas disease) - extremely low
• parvovirus B19 - extremely low
• babesiosis - extremely low
• Borrelia burgdorferi (Lyme disease) - theoretical only
• variant Creutzfeldt-Jacob Disease - extremely low

References

1. Chiavetta J, Escobar,M, Newman A, He Y, Driezen P, Deeks S, Hone D, O’Brien S, Sher G. Incidence and estimated rates of residual risk for HIV, hepatitis C hepatitis B and human T-cell lymphotropic viruses in blood donors in Canada, 1990-2000. CMAJ, Oct. 14, 2003; 169 (8).
2. Kleinman C, Chan P, Robillard P. Risks associated with transfusion of cellular blood components in Canada. Transfus Med Rev 2003 Apr.;17(2):120-62.
3. Peden AH, Head MW, Ritchie DL et al. Preclinical vCJD after blood transfusion in a PRNP codon 129 heterozygous patient. Lancet 2004 Aug 7; 364(9433) 527-9.
4. Llewelyn CA, Hewitt PE, Knight RS et al. Possible transmission of variant Creutzfeldt-Jakob disease by blood transfusion. Lancet 2004 Feb 7;363(9407) 417-21.

Updated: July 2010