The virus can be transmitted by blood transfusion. Although it is not a problem for most transfusion recipients, it can cause serious disease in patients whose immune systems function poorly, such as premature infants and patients who have undergone tissue or organ transplantation. These patients frequently are given blood that has been screened or processed in such a way as to reduce the risk of CMV transmission. HTLV-I is found particularly in Japanese people and in people living in the Caribbean area. HTLV-I can, on occasion, cause leukemia and a paralytic disease of the nervous system, but it takes many years to do so.
Blood is tested for evidence of syphilis infection.
Donors who are at risk of transmitting malaria are screened by medical history and rejected as blood donors. As a result, very few recipients of blood transfusions in the United States develop malaria. Similarly, individuals known to be harboring other infectious diseases are deferred or rejected as blood donors. Approximately 1.9 percent of whole blood units donated are discarded due to positive tests. False positives may occur due to the sensitivity of the testing procedure.