The graph shows that the disease spreads slowly at first, then rapidly, and slowly at the end. This pattern of transmission is most characteristic of a disease spread from one person to the next. When only one person has the disease, the rate of transmission is slow because that person may only meet a few others. But as the number of people with the disease increases, the number of meetings that spread the disease also increase. At this time, the disease can spread very rapidly. The disease spreads more slowly again when there are only a few people remaining that do not have the disease. With foodborne and airborne diseases, the rate of disease spread is most rapid when the disease first arises and the greatest number of possible victims are available. Graphs of foodborne and airborne transmission show the greatest rate of disease spread at the start of the outbreak.
FYI: This isn't my explanation this is the explanation the question gives! :)
