Postdisaster PTSD over four waves of a panel study of Mexico's 1999 flood By: Fran H. Norris, Arthur D. Murphy, Charlene K. Baker, and Julia L. Perilla This is the peer reviewed version of the following article: Norris, F., Murphy, A., Baker, C., Perilla, J. (2004). Postdisaster PTSD over four waves of a panel study of Mexico's 1999 flood. Journal of Traumatic Stress, 17, 283-292. which has been published in final form at https://doi.org/10.1023/B:JOTS.0000038476.87634.9b. This article may be used for non- commercial purposes in accordance with Wiley Terms and Conditions for Use of Self- Archived Versions. ***© 2004 International Society for Traumatic Stress Studies. Reprinted with permission. No further reproduction is authorized without written permission from Wiley. This version of the document is not the version of record. Figures and/or pictures may be missing from this format of the document. *** Abstract: Samples of adults representative of Tezuitlán, Puebla and Villahermosa, Tobasco (combined N = 561), were interviewed 6, 12, 18, and 24 months after the devastating 1999 floods and mudslides in Mexico. Current DSM‐IV PTSD and major depressive disorder (MDD) were assessed with the Composite International Diagnostic Interview. At Wave 1, PTSD was highly prevalent (24% combined), especially in Tezuitlán (46%), which had experienced mass casualties and displacement. Both linear and quadratic effects of time emerged, as PTSD symptoms initially declined but subsequently stabilized. Differences between cities lessened as time passed. Comorbidity between PTSD and MDD was substantial. The findings demonstrate that the international health community needs to be prepared for epidemics of PTSD when disasters strike developing areas of the world. Keywords: disaster | PTSD | depression | Mexico | longitudinal studies Article: A substantial literature on the effects of disasters has accumulated over the past 25 years. These studies allow several tentative conclusions to be reached about the nature of these effects. First, it appears that posttraumatic stress disorder (PTSD) is among the most common adverse consequences for which disaster victims are at risk. Norris et al. (2002) found evidence of PTSD in 109 (68%) of 160 samples that were included in their review. Symptoms of PTSD typically begin soon after the event (e.g., North, Smith, & Spitznagel, 1997; Waelde, Koopman, Rierdan, & Spiegel, 2001) and may persist for years after disasters that are especially severe (e.g., Green et al., 1990; Yule, Bolton, Udwin, O'Ryan, & Nurrish, 2000). Depression is also common in the aftermath of disaster, often occurring in combination with PTSD (e.g., Bolton, O'Ryan, Udwin, Boyle, & Yule, 2000; de la Fuente, 1990; Fullerton, Ursano, Tzu-Cheg, & Bhartiya, 1999; Lima,