Final answer:
No specific family member should be universally restricted from visiting a leukemia patient solely based on their relation. The decision should consider the health and exposure history of the individual family members to reduce infection risk for the patient.
Step-by-step explanation:
The question centers on infection control for a patient with newly diagnosed leukemia. In leukemia patients, the immune system is compromised due to the disease itself and the treatments such as chemotherapy. Therefore, it is paramount to protect these patients from potential infections that could be brought in by visitors. Although there is no specific family member that should be universally restricted from visiting, the main consideration is whether the visitor might pose an infection risk due to recent illness, presence of communicable disease, or vaccinations with live viruses. It's also important to follow the hospital's infection control policies which may vary depending on recent outbreaks or the patient's current state of health.
However, from the choices given (Sibling, Parent, Grandparent, Cousin), without any additional context regarding their health status, none would inherently need to be restricted based solely on their familial relationship. Decisions should be made on a case-by-case basis, assessing the health and recent exposure history of the individual family members.