Similarly, a city in which there is pestilence or collapse [of buildings], that city must fast and sound [the shofar], and all surrounding areas fast but do not sound [the shofar]. R' Akiva says: They sound [the shofar] but do not fast. What is considered pestilence? [In] a city that can bring forth five hundred [men] on foot, [if] three [men] died on three successive days, it is considered pestilence. Fewer than this is not considered pestilence.