Final answer:
The slow progression of Kayla's symptoms suggests a non-infectious cause, as conditions like bacterial meningitis would typically lead to rapid symptom onset, which was not observed in Kayla's case.
Step-by-step explanation:
One reason why Kayla's symptoms are not likely due to an infectious agent is the rate of progression of her symptoms. Infectious agents, such as those causing bacterial meningitis, typically lead to a more rapid onset and progression of symptoms. Since Kayla's condition did not worsen rapidly and because meningitis usually shows severe symptoms quickly, her condition might be attributed to non-infectious causes such as autoimmune disorders like systemic lupus erythematosus (SLE) or amyotrophic lateral sclerosis (ALS).