Akl et al. BMC Public Health 2011, 11:244 http://www.biomedcentral.com/1471-2458/11/244 increased incidence of low birth weight and pulmonary problem in newborns of mothers smoking waterpipe [39-41]. Another feature that might have contributed to the rise of waterpipe smoking is its higher social acceptabil- ity compared with cigarette smoking. In many settings, particularly in Middle Eastern countries and commu- nities, waterpipe smoking is practiced during social activities whereby family members and friends smoke together [59]. Indeed, a number of studies showed that smoking in the house, [3,26-28,38,60,61] smoking in the family [11,25,46-48] and smoking among friends [11,25-28,48] are associated with waterpipe smoking among school students and university students. A pattern of spread of waterpipe smoking appears to be through immigration. Indeed, while Middle Eastern coun- tries had some of the highest prevalence of waterpipe smoking [3,15-33,35-45,60-64], in certain Western coun- tries (e.g. USA, Australia) groups of Middle Eastern des- cent had the highest prevalence of waterpipe smoking [11-13,46-52]. These observations suggest that immigrant groups tend to maintain some of their culture specific health behaviors such as waterpipe smoking [65,66]. Moreover, immigrant groups might also pass on these behaviors to other groups as suggested by the significant prevalence of waterpipe smoking among non-Middle East- ern groups in these Western countries [11-13,46-52]. However, this pattern has not been found in certain Eur- opean countries with very high prevalence of waterpipe use such as Estonia, Denmark, Sweden, and Germany [67]. As stated above, waterpipe tobacco smoking was con- sistently more common in school and university stu- dents than in adults in countries in which surveys were conducted. In the absence of longitudinal data, it is not clear whether these results reflect a time trend of age specific prevalence. If age specific prevalence has not been increasing, the above observation suggests that adolescents tend to quit waterpipe smoking as they age into adulthood. If age specific prevalence has been increasing, this suggests that school and university stu- dents have been affected the most and we might see a cohort effect of increasing prevalence among adults as these younger individuals age. Indeed, there is emerging evidence that waterpipe use predicts regular cigarette smoking, at least among Danish youth [67]. Conclusion Public health agencies need to recognize the burgeoning prevalence of waterpipe tobacco smoking particularly among the youth and ensure the comprehensiveness of their tobacco control strategies. These strategies could include those proven to be effective with cigarette smok- ing, i.e., stricter regulation of advertisement and age restriction on sales. Awareness campaigns should to be Page 10 of 12 tailored to the prevailing belief systems and based on and culturally sensitive assessments of the roots of waterpipe tobacco smoking. Surveillance programs would help in monitoring the effectiveness of public health policies and strategies put in place. There is a need for longitudinal nationally representa- tive studies to better understand the epidemiology of this new epidemic particularly in terms of the mainte- nance of waterpipe smoking after teen age and the role of waterpipe as a gateway for future cigarette smoking and assist public health agencies in developing and applying control policies and strategies. Qualitative stu- dies would be extremely helpful in understanding the misconceptions about waterpipe smoking and the rela- tionship between waterpipe smoking and the initiation of cigarette smoking particularly among the youth. On the other hand, future studies need to be of higher methodological quality and particularly use validated tools. There is also a need to standardize the methods of reporting the prevalence (waterpipe only smokers ver- sus all waterpipe smokers) and the type(s) of measure of waterpipe smoking (e.g. current, ever, and regular). Additional material Additional file 1: Electronic search strategies. Provides the detailed search strategies used in the systematic review Additional file 2: Excluded studies. Provides a list of excluded studies and the reason for their exclusion Additional file 3: Tables describing the characteristics of included studies measuring waterpipe smoking prevalence by world region. Provides tables describing the characteristics of included studies measuring waterpipe smoking prevalence by world region Additional file 4: Results of the Global Youth Tobacco Survey (GYTS) and World Health Organization (WHO) surveys. Provides the prevalence of waterpipe smoking in the GYTS and WHO surveys Acknowledgements We would like to thank Drs. Rice, Riachy, Magder, Eissenberg, Chaaya, Grekin, Fadhil, and Tamim for providing additional information; Dr. Andy Symons for assisting in abstracting data; Dr. Ranime Saliba for her assistance; Mr. Ed Leisner and Ms. Michelle Zafron for their help in designing the search strategy; Mr. Nadeem Nazeer for his assistance with producing the maps; and Ann Grifasi for her administrative assistance. This study was not funded. Author details 1Department of Medicine, State University of New York at Buffalo, NY, USA. 2Department of Family Medicine, State University of New York at Buffalo, NY, USA. 3Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton Canada. 4Department of Social and Preventive Medicine, State University of New York at Buffalo, NY, USA. 5Department of Pediatrics, Wayne State University, Detroit, MI, USA. 6Faculty of Health Sciences, University of Balamand, Beirut, Lebanon. Authors’ contributions EAA contributed to drafting the protocol, designing the search strategy, developing the forms, screening, data abstraction, data analysis, and drafting of the manuscript. SKG contributed to data abstraction, data analysis, and drafting of the manuscript. RO and SA contributed to data abstraction. PAJ