Background. This study was designed to evaluate the incidence of acute mountain sickness (AMS) occurring on different climbing routes on Mount Damavand and the effect of beginning time of ascent in Iranian trekkers. Methods. This study was a descriptive cohort investigation, performed in summer 2007. All trekkers who ascended Mount Damavand from northern, western, eastern, and southern paths and passed 4200？m altitude were included in the study. Two questionnaires were completed for each trekker (personal information and Lake Louise score questionnaire). Multiple logistic regression analysis was used to explore the independent predicting variables for AMS. Results. Overall incidence rate of AMS was 53.6%. This rate was the highest in south route (61.5%) ( ). There was no difference in the incidence of AMS on other paths. AMS history, AMS history on Damavand, the beginning time of climbing, sleeping at 4200？m altitude, and home altitude had significant effect on AMS incidence, but by multiple logistic regression analysis south route and AMS history on Mount Damavand had positive effect on incidence of AMS ( and ). Conclusion. The path and the beginning time of ascent can affect incidence of AMS. The risk of occurrence of AMS was 1.9 times as large for trekkers who ascended from southern route. 1. Introduction Acute mountain sickness (AMS) is a disorder which is seen in ascent to altitudes higher than 3000 meters. It is a clinical syndrome with headache and one or more other symptoms including gastrointestinal symptoms (poor appetite, nausea, vomiting), fatigue and/or weakness, dizziness/lightheadedness, and sleep disturbances [1, 2]. Its diagnosis is based on environmental symptom questionnaires, Hackett or Lake Louise AMS score [3, 4]. Several studies in different countries have been done so far, and incidence rates have been reported from 25% to 69% [2, 5–11]. Some effective factors have been considered in several studies, such as change of altitude related to residence altitude [3, 5, 11], speed of mountain climbing [1, 2, 11], very low and very high range of ages [5, 12], positive history of mountain sickness [8, 11], beginning mountain climbing at night [11], sleep in altitudes more than 3 hours in altitude [1], and water and fluid intake [13]. However, the relation of some factors like age and gender to the incidence of the disease is in doubt. Mount Damavand has four main paths for mountaineers’ ascent. In our previous study, the incidence rate of disease was seen in more than 60% of mountaineers who ascend from the south [11]. Iranian expert
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