Bacterial infection from contaminated blood or blood products is rare as long as continuous adequate refrigeration is provided. Platelets are especially apt to develop bacterial growth when stored at room temperature. The spirochetes of syphilis usually die after refrigerated storage for 4-5 days. Malaria could be transmitted in blood from infected travelers or immigrants from endemic areas. Virus infections are a much greater problem. These infections are discussed in detail in Chapter 17 and will be mentioned only briefly here.

Hepatitis virus infection. This subject is discussed more completely in Chapter 17. Transfusion-related hepatitis virus infection used to occur in about 10% of transfused patients (range, 0.02-25%) and as high as 50% in those who received many transfusions. However, only about 10% of these infections were symptomatic. An estimated 90% of life-threatening viral infections have been eliminated by pretransfusion donor testing for hepatitis virus B and C, human immunodeficiency virus-1 and 2 (HIV-1 and 2), and human T-cell leukemia virus-I and II (HTLV-I and II). About 5%-10% of transfusion-related hepatitis virus infections are now due to hepatitis B. Mandatory screening of donor blood for hepatitis B surface antigen (HBsAg) and the core antibody (HBcAb), in addition to attempts to eliminate high-risk carrier groups among donors by careful questioning and reliance on nonpaid volunteer donors, has eliminated more than 90% of hepatitis B transfusion-related infections. Use of frozen RBCs was originally thought to eliminate hepatitis B virus infectivity, but this has proven to be untrue, although the incidence of transmission may be somewhat reduced. Therefore, whole blood, packed RBCs, and some blood products can transmit hepatitis virus infection. In general, single-donor products are less likely to carry infection than pooled-donor products. Two percent to 12% of persons who test positive for HBsAg are also carriers of delta hepatitis virus (hepatitis D virus), a virus that requires a liver cell already infected by hepatitis B to replicate. Therefore, a small percentage of patients infected by hepatitis B virus develop superimposed hepatitis D virus. Serologic tests for hepatitis D virus are now available. A very small number of transfusions carry hepatitis A virus.

It is not currently recommended to give either immune human serum globulin or hepatitis B immune globulin (HBIG) to prevent hepatitus B virus (HBV) or HIV infections. Neither have prevented HBV infection in the virus dose received from transfusion; and the evidence to date regarding hepatitus C virus (HCV) is conflicting. Albumin or immune globulin have not been reported to cause HIV or hepatitis virus infection.

Currently, about 85%-90% of transfusion-related hepatitis virus infections are due to HCV. The carrier rate for HCV in the volunteer donor population is said to be about 1.5%. Before a serologic test for HCV antibody was available, blood banks tried to eliminate donor blood that might contain HCV by testing donors for alanine aminotransferase (ALT, formerly SGOT), which is usually elevated in active hepatitis virus infection, and for HBV core antibody, which is associated with about a 3-fold increased incidence of HCV in addition to indicating HBV. These two tests were thought to eliminate about one third of donor blood carrying HCV. When HCV antibody tests first became available, sensitivity of the tests was estimated to be about 50% and the tests produced about 50% false positive reactions. The third generation HCV antibody tests available in 1993 appear to have 80% sensitivity and less than 10% false positive results.

Cytomegalic inclusion virus. After hepatitis virus, the most frequent transfusion-related virus infection is cytomegalovirus (CMV). The carrier rate for CMV in the donor population is reported to be 6%-12%, whereas 35%-70% of donors have antibody to CMV. The percentage of infected persons who develop symptoms is not well documented, but most of those who have symptoms display an illness clinically resembling infectious mononucleosis (“heterophil-negative mononucleosis”). The disease is most serious when contracted by immunocompromised persons, transplant patients, and premature infants of low birth weight. Serologic tests for CMV antibody are now available and are used by some institutions to screen donor blood intended for low birth weight newborns and some immunocompromised persons. Since CMV is carried by WBCs, washed RBCs and frozen RBCs are reported to have a lower incidence of CMV infection than standard packed RBCs. However, best results are obtained with special leukocyte removal filters.

Human immunodeficiency virus. The third important virus group is the HIV-I, the cause of acquired immunodeficiency syndrome (AIDS) and the various pre-AIDS conditions. Studies have indicated a 65%-70% rate of recipient infection (based on appearance of HIV-I antibody in recipients) from antibody-positive donor blood. Until 1986, about 2% of AIDS was due to transfusion of blood or blood products. Current mandatory donor blood screening tests for HIV-I antibody plus attempts to persuade high-risk persons not to donate are thought to have eliminated well over 95% of infected donor blood. Heat treatment of factor VIII concentrate also reduces the incidence of HIV-I transmission; this plus donor testing has virtually eliminated factor VIII concentrate infectivity by HIV-I. Unfortunately, heat treatment does not affect hepatitis virus infectivity. Therapeutic immune globulin is also free of HIV infectivity due to the way it is prepared, although the preparations may contain detectable antibody against HIV-I. This passively transferred antibody may be responsible for a false positive HIV-I antibody test result, which may persist for as long as 6 months, if the recipient is tested for HIV antibodies. More recently, another member of the HIV family called HIV-2 was discovered in Africa; after it began spreading elsewhere, tests were developed and mandated for blood bank use.

HTLV-I, which causes human T-cell leukemia, and HTLV-II, which may be associated with hairy cell leukemia (Chapter 7), can also be transmitted by transfusion. Transmission of HTLV-I could be a problem in donor blood from endemic areas, such as Japan and the Caribbean. Tests for HTLV-I and II are also now in use in blood banks. Finally, other viruses, such as the Epstein-Barr virus, can also be transmitted by transfusion.