For epidemics with two or more phases, a variation of the S-shaped Richards model has been proposed [6] . This multi-staged Richards model distinguishes between two types of turning points: the initial S curve which signifies the first turning point that ends initial exponential growth; and a second type of turning point in the epidemic curve where the growth rate of the number of cumulative cases begins to increase again, signifying the beginning of the next epidemic phase. This variant of Richards model provides a systematic method of determining whether an outbreak is single-or multi-phase in nature, and can be used to distinguish true turning points from peaks and valleys resulting from random variability in case counts. More details on application of the multi-staged Richards model to SARS can be found in [6, 7] . Readers are also referred to [8, 9] for its applications to dengue.