Factors predisposing to serious neurologic damage include Increasing age (throughout life) Recent tonsillectomy or intramuscular injection Pregnancy Impairment of B-cell function Physical exertion concurrent with onset of the central nervous system phase Poliovirus is present in the throat and feces during incubation and, after symptom onset, persists 1 to 2 weeks in the throat and ≥ 3 to 6 weeks in feces.