Select the correct answer. A doctor in a rural town diagnoses a patient with a rare viral infection. Immediately after diagnosing the patient, the doctor reports the infection as a disease outbreak to the Centers for Disease Control and Prevention. Which of these factors most likely led to the doctor's actions?

A.
The patient recently visited his mother in a neighboring state.
B.
The patient exhibited severe symptoms that have been ongoing for several days.
C.
No patients have been diagnosed with this type of infection in 30 years.
D.
The patient's lab results indicated that his white blood cell count was high.