Surprisingly to me, it appears like Bell's Palsy is a not uncommon condition.
Based on SF anecdotal information alone, it's clear why 4 cases in 22,000 isn't being considered an unusual number.
Of course, the CDC is wise to monitor for it (as they should) but it's understandable why they're not alarmed, given how many folks in this little thread have had BP strike in their families or circle of close friends.