Final answer:
Immediate isolation is necessary for a patient exhibiting symptoms of meningococcal disease, such as high fever, stiff neck, and petechial rash, due to its high contagiousness and severity.
Step-by-step explanation:
The medical assistant should prioritize immediate isolation for the patient reporting a high fever, stiff neck, blurry vision, and petechial rash. These symptoms are highly suspicious of meningococcal disease, which is a severe and potentially life-threatening infection caused by the bacteria Neisseria meningitidis. This condition is highly contagious and requires prompt isolation and medical intervention.
The other conditions listed, including a patient with MRSA and a new wound, a patient with VRE of the GI tract, and a patient with a fever and rash who has never had chickenpox, while concerning and requiring appropriate precautions, do not present with the same immediate level of communicable risk as the symptoms of meningococcal disease.