title: Acute mountain sickness among tourists visiting the high-altitude city of Lhasa at 3658 m above sea level: a cross-sectional study.
abstract: BACKGROUND
  Traveling to Tibet implies a risk for developing acute mountain sickness (AMS), and the size of this problem is likely increasing due to the rising number of tourists. No previous study on AMS has been conducted among the general tourist population in Tibet. Thus, the aim of this study was to estimate the prevalence and determinants of AMS in a large tourist population visiting Lhasa.
  
  
  METHODS
  A sample of 2385 tourists was recruited from seven randomly selected hotels in Lhasa between June and October 2010. Within three days of their first arrival, the participants filled in a questionnaire based on the Lake Louise Scoring System (LLSS) about AMS-related symptoms and potential contributing factors. AMS was defined as the presence of headache and a cumulative Lake Louise Score ≥4. After estimating the prevalence of AMS, a Log-Binomial Model was applied to analyse the relationship between AMS and selected risk factors.
  
  
  RESULTS
  The prevalence of AMS was 36.7 % (95 % CI: 34.6-38.7 %) and was not dependent on tourists' country of origin. Among the participants who developed AMS, 47.6 % reported that they experienced symptoms within the first 12 h after arriving in Lhasa, and 79.0 % reported that they had to reduce their activity level. A poor or average health condition (adjusted PR 1.63, 95 % CI 1.38-1.93), an age below 55 years (adjusted PR 1.29, 95 % CI 1.04-1.60), a rapid ascent to Lhasa (adjusted PR 1.17, 95 % CI 1.02-1.34) were independent AMS risk factors, while smoking (adjusted PR 0.75, 95 % CI 0.59-0.96) and pre-exposure to high altitude (adjusted PR 0.71, 95 % CI 0.60-0.84) reduced the risk of AMS.
  
  
  CONCLUSIONS
  AMS is commonly experienced by tourists visiting Lhasa Tibet, and often affects their activities. The tourists' country of origin did not seem to affect their risk of AMS, and their age was inversely related to AMS. Subjects planning to visit a high-altitude area should be prepared for experiencing AMS-related problems, and consider preventive measures such as pre-exposure or a gradual ascent to high altitudes.
authors.affiliation: Institute of Health and Society, University of Oslo, P.O. Box 1130 Blindern, Oslo, 0318 Norway ; Tibet University Medical College, No. 1 South Luobulinka Road, Lhasa, 850002 Tibet China.
authors.lastname: Gonggalanzi
authors.affiliation: Tibet University Medical College, No. 1 South Luobulinka Road, Lhasa, 850002 Tibet China.
authors.lastname: Labasangzhu
authors.affiliation: Institute of Health and Society, University of Oslo, P.O. Box 1130 Blindern, Oslo, 0318 Norway ; Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Per
authors.initials: P
authors.lastname: Nafstad
authors.affiliation: Institute of Health and Society, University of Oslo, P.O. Box 1130 Blindern, Oslo, 0318 Norway ; Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Hein
authors.initials: H
authors.lastname: Stigum
authors.affiliation: National Key Laboratory of High-Altitude Medicine, Qinghai, China.
authors.forename: Tianyi
authors.initials: T
authors.lastname: Wu
authors.affiliation: Institute of Health and Society, University of Oslo, P.O. Box 1130 Blindern, Oslo, 0318 Norway.
authors.forename: Øyvind Drejer
authors.initials: ØD
authors.lastname: Haldorsen
authors.affiliation: Institute of Health and Society, University of Oslo, P.O. Box 1130 Blindern, Oslo, 0318 Norway.
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Ommundsen
authors.affiliation: Institute of Health and Society, University of Oslo, P.O. Box 1130 Blindern, Oslo, 0318 Norway.
authors.forename: Espen
authors.initials: E
authors.lastname: Bjertness
keywords: Acute mountain sickness; Tibet; Tourist