Fig. 1.

Temporal patterns of DHF in three representative Thai changwats (provinces) over the period 1981–2004. (a–d) Time series data for centrally located changwat 10 (Bangkok, lat 13°72′). (e–h) Data for northern changwat 65 (Phitsanulok, lat 17°03′). (i–l) Data for southern changwat 84 (Surat Thani, lat 9°02′). (a, e, and i) Annual DHF incidence per 100,000 (black). Gray lines show average annual DHF incidence per 100,000 over a 5-year sliding window. (b, f, and j) Wavelet plots of DHF incidence patterns, showing transitions from a short (≈2-year) cycle to a longer-period (≈4-year) cycle in all three changwats. (c, g, and k) Average age of DHF cases. (d, h, and l) Estimated R₀ trajectories over the period 1981–2004, computed from the average age of DHF cases (SI Appendix). DHF incidence and age data were obtained from the Ministry of Public Health of Thailand, as reported elsewhere (58). Wavelet analyses were performed on log-transformed incidence data, by using the Morlet wavelet. Wavelet software was provided by C. Torrence and G. Compo and is available at http://paos.colorado.edu/research/wavelets.