Second, seasonality that was evaluated using the effective reproduction number, R(t), defined as the actual average number of secondary cases per primary case at calendar time t. R(t) shows a time-dependent variation with a decline in susceptible individuals (intrinsic factors) and with the implementation of control measures (extrinsic factors). If R(t) < 1, it suggests that the epidemic is in decline (vice verca, if R(t) > 1). This approach was employed to clearly show the seasonal patterns of transmission and to partly address the issue of dependence among cases, that is, statistically, the observation of an infected individual is not independent of other infected individuals, since the disease is transmitted directly from human to human.