Many Japanese companies had hardly finished announcing their dismal earnings results in March when a new economic threat began to emerge — a flu epidemic that would strike the nation with alarming speed.

The number of confirmed swine flu cases has exploded a week since the first case was discovered at Narita International Airport, so far sickening mostly students or those predisposed to illness.

The speed with which the virus has spread has shocked the public, which is buying up face masks at a swift pace in the belief they will offer some protection from the flu.