Which of the following patients would be at risk of infection due to a decreased WBC count?

A decreased white blood cell (WBC) count, also known as leukopenia, significantly increases the risk of infection since WBCs play a crucial role in the immune system by defending the body against pathogens.

In the case of an AIDS patient, the disease itself is known to compromise the immune system, often leading to a reduction in WBCs. This weakened immune response makes them particularly vulnerable to opportunistic infections, which are infections that occur more frequently and are more severe in individuals with weakened immune systems.

While a cancer patient on chemotherapy is also at risk of infection due to the effects of treatment reducing WBC count, the specific mention of the AIDS patient's leukopenia highlights their already compromised condition due to the virus's impact on immune function.

Older adults can have a natural decline in immune function but they do not automatically present with decreased WBC counts unless other underlying health issues are present. Similarly, pediatric patients generally have robust immune systems, although certain conditions may increase their risk.

Therefore, identifying the AIDS patient, who has leukopenia as a direct consequence of the disease, emphasizes the particular danger they face regarding infections.