Final answer:
A patient with AIDS succumbs to pneumonia due to a severely weakened immune system, caused by a significant reduction in CD4 T-cells from HIV, which renders the body highly susceptible to opportunistic infections that a healthy immune system could otherwise fend off.
Step-by-step explanation:
The reason a client with acquired immunodeficiency syndrome (AIDS) would succumb to pneumonia, while a healthy person who is exposed to the same pneumonia may not, is due to the compromised state of the patient's immune system. In AIDS, which is caused by the human immunodeficiency virus (HIV), there is a significant reduction in CD4 T-cells, which are crucial for mounting an effective immune response. This leaves the body vulnerable to opportunistic infections, such as Pneumocystis pneumonia, which can be fatal due to the immune system's inability to combat them.
Patients with AIDS may also develop additional debilitating conditions, like HIV wasting syndrome, which further weakens the body, making it even more susceptible to infections. Furthermore, the presence of these opportunistic diseases, along with other systemic symptoms like fever, weight loss, and swollen lymph nodes, contribute to the deterioration of a person with AIDS, making their prognosis much worse compared to a healthy individual facing pneumonia.