E-cigarette use and respiratory symptoms in adults: A systematic review and meta-analysis.

"CONFLICTS OF INTEREST The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none was reported."

"FUNDING There was no source of funding for this research."

"A systematic review of the empirical literature was conducted by following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol (Supplementary file) . We have assessed the prevalence of respiratory symptoms among three groups; these groups included exclusive e-cigarette users, dual users (both e-cigarette and traditional cigarette users), and former smokers transitioning to e-cigarettes in an attempt to quit smoking. Therefore, we conducted a meta-analysis to examine the differences in respiratory symptom incidences among these three groups. The protocol for this study was registered with PROSPERO (#CRD42020165973). METHODS: Databases searched included PubMed, CINAHL, Cochrane Library, Embase, and Scopus. We included all English-language, empirical quantitative articles that explored the prevalence of e-cigarette-related respiratory symptoms. Random-effects models were utilized in conducting the meta-analyses. The quality of identified studies was evaluated using the NIH Study Quality Assessment Tools. This study is registered with PROSPERO(#CRD42020165973)."