Final answer:
The primary cause of death in patients with chronic lymphocytic leukemia is infectious complications arising from secondary immunodeficiency caused by the leukemia and chemotherapy treatments.
Step-by-step explanation:
The most common cause of death in patients with chronic lymphocytic leukemia (CLL) is infectious complications due to secondary immunodeficiency. This immunodeficiency is a result of both the leukemia itself, which causes an abnormal overproduction of nonfunctional leukocytes, and the effects of chemotherapy treatments. These treatments further compromise the immune system's ability to combat infections. Patients with CLL and those undergoing chemotherapy are especially susceptible to opportunistic infections from bacteria (such as Staphylococcus), viruses (like enteroviruses), protozoa (including Pneumocystis and Giardia), and fungi (such as Candida). These infections can lead to serious respiratory complications like bacterial pneumonia, which can be fatal when the body's defenses are weakened. It is essential to monitor for signs of infection in patients with CLL and to provide prompt medical intervention to manage any complications.